Selection versus Merge Sorting Trouble

Question

Suppose we have inefficient implementation of swap(a,b)(very costly) function and we are given the choice of four sorting algorithms to choose from, namely:

1. merge-sort
2. selection-sort
3. insertion-sort
4. heap-sort

Which one of the following four will perform the best ?

Now according to me as the swap is a costly operation we need to minimise the number of swaps. so technically the answer should be merge sort as it performs no swapping in its general implementation. But the answer-key suggests that it must be selection-sort instead ? I fail to understand why, please help.

Selection sort first finds the correct index and then swaps which is economical but doesn't merge sort perform better still ?