from fractions import Fraction
from heapq import*

MOD=998244353
T=int(input())
for _ in range(T):
    N,K=map(int,input().split())
    A=list(map(int,input().split()))
    hq=[-Fraction(A[i],1) for i in range(N)]
    heapify(hq)
    ans=pow(sum(A),-K,MOD)
    for i in range(K):
        nf=heappop(hq)
        ans*=(i+1)
        ans*=-nf.numerator
        ans*=pow(nf.denominator,-1,MOD)
        ans%=MOD
        heappush(hq,Fraction(nf.numerator,nf.denominator+1))
    print(ans)