A.middle=(high-low)/2;MergeSort(A,low,middle);MergeSort(A,middle+1,high)
B.middle=(low+high)/2;MergeSort(A,low,middle);MergeSort(A,middle+1,high)
C.middle=(low+high)/2;MergeSort(A,middle+1,high);MergeSort(A,low,middle)
D.middle=(high-low)/2;MergeSort(A,middle+1,high);MergeSort(A,low,middle)