4. (10 points) Answer the following short answer questions: (a) (5 points) What is the smallest possible depth of a leaf in a decision tree for s comparison sort? Give a reason for your answer. (Recall the depth of a node in a tree is the number of edges from the root of the tree to the node.) (b) (5 points) Show that quicksort's best-case running time is 2(nlgn)