def cmb(n, r, p):
  if (r < 0) or (n < r):
    return 0
  r = min(r, n - r)
  return fac[n]*finv[r]*finv[n-r]%p

def perm(n,r,p):
  if (r < 0) or (n < r):
    return 0
  return fac[n]*finv[n-r]%p

N = 2*pow(10,5) + 1000
MOD = 998244353

fac = [-1]*(N+1); fac[0] = 1; fac[1] = 1 #階乗
finv = [-1]*(N+1); finv[0] = 1; finv[1] = 1 #階乗の逆元
inv = [-1]*(N+1); inv[0] = 0; inv[1] = 1 #逆元
for i in range(2,N+1):
  fac[i] = fac[i-1]*i%MOD
  inv[i] = MOD - inv[MOD%i]*(MOD//i)%MOD
  finv[i] = finv[i-1]*inv[i]%MOD

#print(cmb(5, 4, MOD))

def main():
    T = int(input())
    for _ in range(T):
        N,K = map(int,input().split())
        A = list(map(int,input().split()))
        S = sum(A)
        A.sort(reverse=True)
        num = [0]*N
        nokori = K
        for i in range(N):
            num[i] += K*A[i]//S
            nokori -= num[i]
        #print(num)
        idx = 0
        while nokori > 0:
            num[idx] += 1
            nokori -= 1
            idx += 1
        #print("UP",num)
        

        def calc(A,B,mod=998244353):
            k = sum(B) #回数
            s = sum(A) #全ての和
            chi = 1
            par = pow(s,k,mod)
            for i in range(len(A)):
                chi *= pow(A[i],B[i],mod)*cmb(k,B[i],mod)
                chi %= mod
                k -= B[i] #残りの回数が減る
            #print(chi,par)
            ret = chi*pow(par,mod-2,mod)
            ret %= mod
            return ret

        #for i in range(10):
        #    for j in range(10):
        #        for k in range(10):
        #            for l in range(10):
        #                num = [i,j,k,l,10-(i+j+k+l)]
        #                ans = calc(A,num)
        #                if ans == 484466660:
        #                    print(num)

        ans = calc(A,num)
        print(ans%MOD)



if __name__ == '__main__':
    main()