#include<bits/stdc++.h>
#include<ext/pb_ds/assoc_container.hpp>
#include<ext/pb_ds/hash_policy.hpp>
#define Add(x, y) (x + y >= mod) ? (x + y - mod) : (x + y)
#define lowbit(x) x & (-x)
#define pi pair<ll, ll>
#define pii pair<ll, pair<ll, ll>>
#define iip pair<pair<ll, ll>, ll>
#define ppii pair<pair<ll, ll>, pair<ll, ll>>
#define ls(k) k << 1
#define rs(k) k << 1 | 1
#define fi first
#define se second
#define full(l, r, x) for(auto it = l; it != r; ++it) (*it) = x
#define Full(a) memset(a, 0, sizeof(a))
#define open(s1, s2) freopen(s1, "r", stdin), freopen(s2, "w", stdout);
#define For(i, l, r) for(register int i = l; i <= r; ++i)
#define _For(i, l, r) for(register int i = r; i >= l; --i)
using namespace std;
using namespace __gnu_pbds;
typedef double db;
typedef unsigned long long ull;
typedef long long ll;
bool Begin;
const int N = 81, M = 1e4 + 10, mod = 1e9 + 7;
inline ll read(){
    ll x = 0, f = 1;
    char c = getchar();
    while(c < '0' || c > '9'){
        if(c == '-')
          f = -1;
        c = getchar();
    }
    while(c >= '0' && c <= '9'){
        x = (x << 1) + (x << 3) + (c ^ 48);
        c = getchar();
    }
    return x * f;
}
inline void write(ll x){
	if(x < 0){
		putchar('-');
		x = -x;
	}
	if(x > 9)
	  write(x / 10);
	putchar(x % 10 + '0');
}
ll n, c, sum;
ll a[N], dp[M][N];
inline ll qpow(ll a, ll b){
	ll ans = 1;
	while(b){
		if(b & 1ll)
		  ans = (ans * a) % mod;
		a = (a * a) % mod;
		b >>= 1ll;
	}
	return ans;
}
bool End;
int main(){
	n = read(), c = read();
	for(int i = 1; i <= n; ++i){
		a[i] = read();
		sum = (sum + qpow(a[i], c)) % mod;
	}
	for(int i = 1; i <= n; ++i)
	  dp[0][i] = 1;
	for(int i = 1; i <= c; ++i)
	  for(int j = 1; j <= n; ++j)
		for(int k = 1; k <= j; ++k)
		  dp[i][j] = (dp[i][j] + a[k] * dp[i - 1][k] % mod) % mod;
	write((dp[c][n] - sum + mod) % mod);
	cerr << '\n' << abs(&Begin - &End) / 1048576 << "MB";
	return 0;
}