C++ Data Structures, please explain the steps so I can understand the answer.

1 Read the following Heap Sort function and determine the correct answer for blank #4. template void Heap Sort(Item Type values[], int numValues) // Pre: Struct Heap Type is available. // Post: The elements in the array values are sorted by key. { int index // Convert the array of values into a heap. for (index = index >= 0; index--) // 1 (values, index, numValues-1); // 2 // Sort the array for (index = numValues-1; index >=1; index--) { Swap values[index]); // 3 _(values, 0, index-1); // 4 } } ReheapUp ReheapDown