下述代码实现素数表的埃拉托色尼(埃氏)筛法，筛选出所有小于等于n的素数。

下面说法，正确的是（    ）。

vector<int> sieve_Eratosthenes(int n) {

      vector<bool> is_prime(n +1, true);

      vector<int> primes;

      for (int i = 2; i * i <= n; i++) {

            if (is_prime[i]) {

                  primes.push_back(i);

                  for (int j = i * i; j <= n; j += i) {

                        is_prime[j] = false;

                  }

            }

      }

      for (int i = sqrt(n) + 1; i <= n; i++) {

            if (is_prime[i]) {

                  primes.push_back(i);

            }

      }

      return primes;

}