#include <bits/stdc++.h>
using namespace std;
const int mod = 1e9 + 7;
const int maxn = 2e5 + 10;
int n, k;
long long fac[maxn + 10], afac[maxn + 10];
long long qpow(long long a, long long b) {
  long long ret = 1LL;
  while (b) {
    if (b & 1) ret = ret * a % mod;
    a = a * a % mod;
    b >>= 1;
  }
  return ret;
}
long long inv(long long x) { return qpow(x, mod - 2); }
void Pre() {
  fac[0] = 1LL;
  for (int i = 1; i <= maxn; i++) fac[i] = fac[i - 1] * (long long)i % mod;
  afac[maxn] = inv(fac[maxn]);
  for (int i = maxn; i >= 1; --i) afac[i - 1] = afac[i] * i % mod;
}
long long C(long long n, long long m) {
  if (m > n) return 0;
  return fac[n] * afac[n - m] % mod * afac[m] % mod;
}
void solve() {
  vector<pair<int, int> > h;
  int l, r;
  for (int i = 1; i <= n; i++) {
    scanf("%d %d", &l, &r);
    h.push_back(make_pair(l - 1, 1));
    h.push_back(make_pair(r, -1));
  }
  sort(h.begin(), h.end());
  long long cnt = 0LL, ans = 0LL;
  int pos = h[0].first;
  for (int i = 0; i < h.size(); i++) {
    long long tmp = C(cnt, k) * (h[i].first - pos) % mod;
    ans = (ans + tmp) % mod;
    cnt += 1LL * h[i].second;
    pos = h[i].first;
  }
  printf("%I64d\n", ans);
}
int main() {
  Pre();
  while (scanf("%d %d", &n, &k) != EOF) {
    solve();
  }
  return 0;
}
