Exercise 2.16 For each of the following languages L S {a,b}", find a regular expression representing it: a) All strings that contain exactly one a. b) All strings that contain exactly two a's. c) All strings that contain at least two a's. d) All strings that begin with aa. e) All strings that begin with aa and end with bb. f) All strings that do not begin with aa. g) All strings that contain the substring aaa or the substring bbb. h) All strings that contain the substring aa and the substring bb. i) All strings, where every occurrence of a is followed immediately by a b (in other words, all strings that contain no occurrence of aa)