#include<iostream>
#include<queue>
#include<atcoder/modint>
using namespace std;
using mint=atcoder::modint998244353;
int T,N,K;
int A[1<<17];
mint inv[1<<17];
main()
{
	cin>>T;
	inv[1]=1;
	for(int i=2;i<1<<17;i++)inv[i]=-(998244353/i)*inv[998244353%i];
	for(;T--;)
	{
		cin>>N>>K;
		int sum=0;
		priority_queue<pair<int,pair<int,int> > >P;
		for(int i=0;i<N;i++)
		{
			cin>>A[i];
			P.push(make_pair(A[i]*K,make_pair(0,A[i])));
			sum+=A[i];
		}
		mint ans=1,invsum=mint(1)/sum;
		for(int i=1;i<=K;i++)
		{
			ans*=i;
			pair<int,pair<int,int> >p=P.top();P.pop();
			p.first-=sum;
			p.second.first--;
			P.push(p);
			ans*=inv[-p.second.first];
			ans*=p.second.second*invsum;
		}
		cout<<ans.val()<<endl;
	}
}