下⾯ merge_sort 函数试图实现归并排序算法，横线处应该填⼊的是（ ）。
#include <vector>
using namespace std;
void merge_sort(vector<int> & arr, int left, int right) {
if (right - left <= 1)
return;
int mid = (left + right) / 2;
merge_sort(________); // 在此处填入选项
merge_sort(________); // 在此处填入选项
vector<int> temp(right - left);
int i = left, j = mid, k = 0;
while (i < mid && j < right)
if (arr[i] <= arr[j])
temp[k++] = arr[i++];
else
temp[k++] = arr[j++];
while (i < mid)
temp[k++] = arr[i++];
while (j < right)
temp[k++] = arr[j++];
for (i = left, k = 0; i < right; ++i, ++k)
arr[i] = temp[k];
}
- A. ```c++
arr, left, mid
arr, mid, right
- **B.** ```c++
arr, left, mid + 1
arr, mid + 1, right
- C. ```c++
arr, left, mid
arr, mid + 1, right
- **D.** ```c++
arr, left, mid + 1
arr, mid + 1, right + 1