A list of $n$ strings, each of length $n$, is sorted into lexicographic order using the merge-sort algorithm. The worst case running time of this computation is

1. Standard merge-sort sorts a list of $n$ elements using $O(n \log n)$ comparisons.

2. In this problem, each element is a string of length $n$. Comparing two strings of length $n$ takes $O(n)$ time in the worst case.

3. Therefore, the worst-case time complexity of merge-sort on $n$ strings of length $n$ is:

   $$T(n) = O(n \log n) \times O(n) = O(n^2 \log n)$$

*Note*: In the official answer key for Paper CS Code A, this question was awarded Marks to All (though in some codes it was marked as option B).