A sorting algorithm is stable if numbers with the same value appear in the output array in the same order as they do in the input array. Are merge-sort, quick-sort, and bubble-sort stable?
a) Merge-sort and quick-sort are stable; bubble-sort is not.
b) Quick-sort is stable; merge-sort and bubble-sort are not.
c) Bubble-sort is stable; merge-sort and quick-sort are not.
d) Merge-sort, quick-sort, and bubble-sort are all stable.