以下C++代码中，符合动态规划规范且能正确求解斐波那契数列第n项（n≥2）的是？

int fib(int n) {
  int dp[n];
  dp[0] = 0;
  dp[1] = 1;
  for(int i = 2; i <= n; i++) dp[i] = dp[i-1] + dp[i-2];
  return dp[n];
}

int fib(int n) {
  vector<int> dp(n + 1);
  dp[0] = 0;
  dp[1] = 1;
  for(int i = 2; i <= n; i++) dp[i] = dp[i-1] + dp[i-2];
  return dp[n];
}

int fib(int n) {
  vector<int> dp(n);
  dp[0] = 0;
  dp[1] = 1;
  for(int i = 2; i < n; i++) dp[i] = dp[i-1] + dp[i-2];
  return dp[n - 1];
}

int fib(int n) {
  int a = 0, b = 1;
  for(int i = 2; i < n; i++) {
    int c = a + b;
    a = b;
    b = c;
  }
  return b;
}