cpp
//组合数2,取值在1e5
//Cab = a! / (a - b)! * b!
#include<iostream>
using namespace std;
using ll = long long;
const ll N = 1e4 + 9, mod = 1e9 + 7;
ll fact[N], infact[N];//阶乘,逆元阶乘
ll qmi(ll a, ll k, ll p)//逆元模板
{
ll res = 1;
while (k)
{
if (k & 1) res = res * a % p;
a = a * a % p;
k >>= 1;
}
return res;
}
int main()
{
ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
fact[0] = infact[0] = 1;
//初始化数组
for (ll i = 1; i < N; ++i)
{
fact[i] = fact[i - 1] * i % mod;
infact[i] = infact[i - 1] * qmi(i, mod - 2, mod) % mod;
}
int n; cin >> n;
while (n--)
{
int a, b; cin >> a >> b;
//多取模的原因是防止超出long long的数据范围
cout << fact[a] * infact[a - b] % mod * infact[b] % mod << '\n';
}
return 0;
}