State a loop invariant for the while loop of lines 12-18 of the merge procedure. Show how to use it, along with the while loops of lines 20-23 and 24-27, to prove that the merge procedure is correct.
a) In each iteration of the loop, the elements in the merged subarray are in sorted order.
b) The loop terminates when the merged subarray is sorted.
c) The loop maintains the invariant that the left and right subarrays are sorted independently.
d) None of the above.