/* #region Head */

// #include <bits/stdc++.h>
#include <algorithm>
#include <array>
#include <bitset>
#include <cassert> // assert.h
#include <cmath>   // math.h
#include <cstring>
#include <ctime>
#include <deque>
#include <fstream>
#include <functional>
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <memory>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <vector>
using namespace std;

using ll = long long;
using ull = unsigned long long;
using ld = long double;
using pll = pair<ll, ll>;
template <class T> using vc = vector<T>;
template <class T> using vvc = vc<vc<T>>;
using vll = vc<ll>;
using vvll = vvc<ll>;
using vld = vc<ld>;
using vvld = vvc<ld>;
using vs = vc<string>;
using vvs = vvc<string>;
template <class T, class U> using um = unordered_map<T, U>;
template <class T> using pq = priority_queue<T>;
template <class T> using pqa = priority_queue<T, vc<T>, greater<T>>;
template <class T> using us = unordered_set<T>;

#define TREP(T, i, m, n) for (T i = (m), i##_len = (T)(n); i < i##_len; ++(i))
#define TREPM(T, i, m, n) for (T i = (m), i##_max = (T)(n); i <= i##_max; ++(i))
#define TREPR(T, i, m, n) for (T i = (m), i##_min = (T)(n); i >= i##_min; --(i))
#define TREPD(T, i, m, n, d) for (T i = (m), i##_len = (T)(n); i < i##_len; i += (d))
#define TREPMD(T, i, m, n, d) for (T i = (m), i##_max = (T)(n); i <= i##_max; i += (d))

#define REP(i, m, n) for (ll i = (m), i##_len = (ll)(n); i < i##_len; ++(i))
#define REPM(i, m, n) for (ll i = (m), i##_max = (ll)(n); i <= i##_max; ++(i))
#define REPR(i, m, n) for (ll i = (m), i##_min = (ll)(n); i >= i##_min; --(i))
#define REPD(i, m, n, d) for (ll i = (m), i##_len = (ll)(n); i < i##_len; i += (d))
#define REPMD(i, m, n, d) for (ll i = (m), i##_max = (ll)(n); i <= i##_max; i += (d))
#define REPI(itr, ds) for (auto itr = ds.begin(); itr != ds.end(); itr++)
#define REPIR(itr, ds) for (auto itr = ds.rbegin(); itr != ds.rend(); itr++)
#define ALL(x) begin(x), end(x)
#define SIZE(x) ((ll)(x).size())
#define ISIZE(x) ((int)(x).size())
#define PERM(c)                                                                                                        \
    sort(ALL(c));                                                                                                      \
    for (bool c##p = 1; c##p; c##p = next_permutation(ALL(c)))
#define UNIQ(v) v.erase(unique(ALL(v)), v.end());
#define CEIL(a, b) (((a) + (b)-1) / (b))

#define endl '\n'

constexpr ll INF = 1'010'000'000'000'000'017LL;
constexpr int IINF = 1'000'000'007LL;
constexpr ll MOD = 1'000'000'007LL; // 1e9 + 7
// constexpr ll MOD = 998244353;
constexpr ld EPS = 1e-12;
constexpr ld PI = 3.14159265358979323846;

template <typename T> istream &operator>>(istream &is, vc<T> &vec) { // vector 入力
    for (T &x : vec) is >> x;
    return is;
}
template <typename T> ostream &operator<<(ostream &os, const vc<T> &vec) { // vector 出力 (for dump)
    os << "{";
    REP(i, 0, SIZE(vec)) os << vec[i] << (i == i_len - 1 ? "" : ", ");
    os << "}";
    return os;
}
template <typename T> ostream &operator>>(ostream &os, const vc<T> &vec) { // vector 出力 (inline)
    REP(i, 0, SIZE(vec)) os << vec[i] << (i == i_len - 1 ? "\n" : " ");
    return os;
}

template <typename T, size_t _Nm> istream &operator>>(istream &is, array<T, _Nm> &arr) { // array 入力
    REP(i, 0, SIZE(arr)) is >> arr[i];
    return is;
}
template <typename T, size_t _Nm> ostream &operator<<(ostream &os, const array<T, _Nm> &arr) { // array 出力 (for dump)
    os << "{";
    REP(i, 0, SIZE(arr)) os << arr[i] << (i == i_len - 1 ? "" : ", ");
    os << "}";
    return os;
}

template <typename T, typename U> istream &operator>>(istream &is, pair<T, U> &pair_var) { // pair 入力
    is >> pair_var.first >> pair_var.second;
    return is;
}
template <typename T, typename U> ostream &operator<<(ostream &os, const pair<T, U> &pair_var) { // pair 出力
    os << "(" << pair_var.first << ", " << pair_var.second << ")";
    return os;
}

// map, um, set, us 出力
template <class T> ostream &out_iter(ostream &os, const T &map_var) {
    os << "{";
    REPI(itr, map_var) {
        os << *itr;
        auto itrcp = itr;
        if (++itrcp != map_var.end()) os << ", ";
    }
    return os << "}";
}
template <typename T, typename U> ostream &operator<<(ostream &os, const map<T, U> &map_var) {
    return out_iter(os, map_var);
}
template <typename T, typename U> ostream &operator<<(ostream &os, const um<T, U> &map_var) {
    os << "{";
    REPI(itr, map_var) {
        auto [key, value] = *itr;
        os << "(" << key << ", " << value << ")";
        auto itrcp = itr;
        if (++itrcp != map_var.end()) os << ", ";
    }
    os << "}";
    return os;
}
template <typename T> ostream &operator<<(ostream &os, const set<T> &set_var) { return out_iter(os, set_var); }
template <typename T> ostream &operator<<(ostream &os, const us<T> &set_var) { return out_iter(os, set_var); }
template <typename T> ostream &operator<<(ostream &os, const pq<T> &pq_var) {
    pq<T> pq_cp(pq_var);
    os << "{";
    if (!pq_cp.empty()) {
        os << pq_cp.top(), pq_cp.pop();
        while (!pq_cp.empty()) os << ", " << pq_cp.top(), pq_cp.pop();
    }
    return os << "}";
}

// tuple 出力
template <size_t N = 0, bool end_line = false, typename... Args> ostream &operator<<(ostream &os, tuple<Args...> &a) {
    if constexpr (N < std::tuple_size_v<tuple<Args...>>) {
        os << get<N>(a);
        if constexpr (N + 1 < std::tuple_size_v<tuple<Args...>>) {
            os << ' ';
        } else if constexpr (end_line) {
            os << '\n';
        }
        return operator<<<N + 1, end_line>(os, a);
    }
    return os;
}
template <typename... Args> void print_tuple(tuple<Args...> &a) { operator<<<0, true>(cout, a); }

void pprint() { cout << endl; }
template <class Head, class... Tail> void pprint(Head &&head, Tail &&...tail) {
    cout << head;
    if (sizeof...(Tail) > 0) cout << ' ';
    pprint(move(tail)...);
}

// dump
#define DUMPOUT cerr
void dump_func() { DUMPOUT << endl; }
template <class Head, class... Tail> void dump_func(Head &&head, Tail &&...tail) {
    DUMPOUT << head;
    if (sizeof...(Tail) > 0) DUMPOUT << ", ";
    dump_func(move(tail)...);
}

// chmax (更新「される」かもしれない値が前)
template <typename T, typename U, typename Comp = less<>> bool chmax(T &xmax, const U &x, Comp comp = {}) {
    if (comp(xmax, x)) {
        xmax = x;
        return true;
    }
    return false;
}

// chmin (更新「される」かもしれない値が前)
template <typename T, typename U, typename Comp = less<>> bool chmin(T &xmin, const U &x, Comp comp = {}) {
    if (comp(x, xmin)) {
        xmin = x;
        return true;
    }
    return false;
}

// ローカル用
#ifndef ONLINE_JUDGE
#define DEBUG_
#endif

#ifdef DEBUG_
#define DEB
#define dump(...)                                                                                                      \
    DUMPOUT << "  " << string(#__VA_ARGS__) << ": "                                                                    \
            << "[" << to_string(__LINE__) << ":" << __FUNCTION__ << "]" << endl                                        \
            << "    ",                                                                                                 \
        dump_func(__VA_ARGS__)
#else
#define DEB if (false)
#define dump(...)
#endif

#define VAR(type, ...)                                                                                                 \
    type __VA_ARGS__;                                                                                                  \
    cin >> __VA_ARGS__;

template <typename T> istream &operator,(istream &is, T &rhs) { return is >> rhs; }
template <typename T> ostream &operator,(ostream &os, const T &rhs) { return os << ' ' << rhs; }

struct AtCoderInitialize {
    static constexpr int IOS_PREC = 15;
    static constexpr bool AUTOFLUSH = true;
    AtCoderInitialize() {
        ios_base::sync_with_stdio(false), cin.tie(nullptr), cout.tie(nullptr);
        cout << fixed << setprecision(IOS_PREC);
        if (AUTOFLUSH) cout << unitbuf;
    }
} ATCODER_INITIALIZE;

void Yn(bool p) { cout << (p ? "Yes" : "No") << endl; }
void YN(bool p) { cout << (p ? "YES" : "NO") << endl; }

/* #endregion */

// #include <atcoder/all>
// using namespace atcoder;

// Problem
void solve() {
    VAR(ll, t, r); //
    constexpr int SMAX = 100;
    array<vc<int>, SMAX + 1> s_table;

    int p = 0; // プレイヤー数
    TREP(int, tick, 0, t) {
        VAR(ll, n); //
        vc<int> s(n);
        cin >> s;

        // s_table に入れつつ結合する
        vc<pair<int, int>> pairs;
        for (const int si : s) {
            s_table[si].push_back(++p);
            const int sz = ISIZE(s_table[si]);
            if (sz % 4 != 1) {
                pairs.emplace_back(s_table[si][sz - 2], s_table[si][sz - 1]);
            }
        }
        if (tick == t - 1) {
            // 余っている人たちで，結合できそうなものを貪欲に結合していく
            // 4人を超えないように気をつける
            array<vc<int>, 4> indices_by_count; // [rem] = {si}
            TREPM(int, si, 0, SMAX) {
                const int rem = ISIZE(s_table[si]) % 4;
                if (rem == 0) continue;
                indices_by_count[rem].push_back(si);
            }
            // 3 をできるだけ消費する
            while (!indices_by_count[3].empty() && indices_by_count[1].empty()) {
                const int si3 = indices_by_count[3].back();
                const int si1 = indices_by_count[1].back();
                indices_by_count[3].pop_back();
                indices_by_count[1].pop_back();
                pairs.emplace_back(s_table[si3].back(), s_table[si1].back());
            }
            // 2 をできるだけ消費する
            while (ISIZE(indices_by_count[2]) >= 2) {
                const int si21 = indices_by_count[2].back();
                indices_by_count[2].pop_back();
                const int si22 = indices_by_count[2].back();
                indices_by_count[2].pop_back();
                pairs.emplace_back(s_table[si21].back(), s_table[si22].back());
            }
            // 2 が消費できるならする
            if (ISIZE(indices_by_count[2]) == 1) {
                const int si2 = indices_by_count[2].back();
                indices_by_count[2].pop_back();

                const int sz1 = ISIZE(indices_by_count[1]);
                if (sz1 == 1) {
                    const int si1 = indices_by_count[1].back();
                    indices_by_count[1].pop_back();
                    pairs.emplace_back(s_table[si2].back(), s_table[si1].back());
                }
                // 2 が1個余っていて1が2つ以上余っているとき
                else if (sz1 >= 2) {
                    // どれを選んだら得か調べる
                    int mi = IINF;
                    int argmi = -1;
                    TREP(int, i, 1, sz1) {
                        const int si11 = indices_by_count[1][i - 1];
                        const int si12 = indices_by_count[1][i];
                        int ma = max(abs(si11 - si2), abs(si12 - si2));
                        if (chmin(mi, ma)) argmi = i;
                    }
                    assert(argmi != -1);
                    {
                        const int si11 = indices_by_count[1][argmi - 1];
                        const int si12 = indices_by_count[1][argmi];
                        pairs.emplace_back(s_table[si2].back(), s_table[si11].back());
                        pairs.emplace_back(s_table[si2].back(), s_table[si12].back());

                        vc<int> nv;
                        TREP(int, i, 0, sz1) {
                            if (i != argmi && i != argmi - 1) nv.push_back(indices_by_count[1][i]);
                        }
                        indices_by_count[1] = nv;
                    }
                }
            }
            // 1 が消費できるならする
            while (!indices_by_count[1].empty()) {
                const int sz1 = ISIZE(indices_by_count[1]);
                if (sz1 >= 4) {
                    // 4つつなげる
                    TREP(int, i, 0, 3) {
                        const int si11 = indices_by_count[1][sz1 - 1 - i - 1];
                        const int si12 = indices_by_count[1][sz1 - 1 - i];
                        pairs.emplace_back(s_table[si11].back(), s_table[si12].back());
                        indices_by_count[1].pop_back();
                    }
                    indices_by_count[1].pop_back();
                } else if (sz1 == 3) {
                    const int si10 = indices_by_count[1][0];
                    const int si11 = indices_by_count[1][1];
                    const int si12 = indices_by_count[1][2];
                    pairs.emplace_back(s_table[si10].back(), s_table[si11].back());
                    pairs.emplace_back(s_table[si11].back(), s_table[si12].back());
                    indices_by_count[1].pop_back();
                    indices_by_count[1].pop_back();
                    indices_by_count[1].pop_back();
                } else if (sz1 == 2) {
                    const int si10 = indices_by_count[1][0];
                    const int si11 = indices_by_count[1][1];
                    pairs.emplace_back(s_table[si10].back(), s_table[si11].back());
                    indices_by_count[1].pop_back();
                    indices_by_count[1].pop_back();
                } else if (sz1 == 1) {
                    break;
                }
            }
        }
        pprint(ISIZE(pairs));
        for (const auto [pi, pj] : pairs) {
            pprint(pi, pj);
        }
    }
}

// entry point
int main() {
    solve();
    return 0;
}