def polymul(f,g):
    lf = len(f)
    lg = len(g)
    res = [0]*(lf+lg-1)
    for i in range(lf):
        for j in range(lg):
            res[i+j] += f[i]*g[j]
            res[i+j] %= MOD
    return res

def fps_nth_term(f,g,N):
    assert g[0] != 0
    while N:
        h = g[:]
        for i in range(1,len(g),2):
            h[i] = -h[i]
        f = polymul(f,h)[N%2:N+1:2]
        g = polymul(g,h)[:N+1:2]
        N //= 2
    return f[0]*pow(g[0],MOD-2,MOD)%MOD

n,c,*a = map(int,open(0).read().split())
MOD = 10**9+7
r = [1]
x = 0
for ai in a:
    r = polymul(r,[1,-ai])
    x -= pow(ai,c,MOD)
print((x+fps_nth_term([1],r,c))%MOD)