i need to know worst case & best case ( Data structures)

These are some examples of combined data structures that you need to select one of them: a) Hash table where each element is a tree. Each tree holds students' data of a specific year. b) Nested hash table. Each table holds students' data of a specific year. c) Tree of hash tables. Each node in the tree holds student's data of a specific year. (a) (D) (c)