Its all because of O (big-oh)


As in the question it is O(n^2) , and according to O notation it is Upper Bound which means Time Compx. can be O(n^2) for the worst case and not more than that, it can be rather less for avg case or even less for the best case.
So (A),(B), and (D) options have TC less than O(n^2), only © which is n^(3-0.5)=n^(2.5) is > n^2.
Hope it helps !!!