For each of the following languages, write a regular expression that describes the language.

Using textbook RegEx notation (character, for empty string, space for concat, | for or, * for zero or more concats)

(a) (7 pts) The set of strings of length three or more, over alphabet {a, b}.

(b) (7 pts) The set of natural numbers divisible by 25.

(c) (7 pts) The set of strings that consist of an odd number of as, over alphabet {a}.

(d) (7 pts) The set of strings over alphabet {a, b} that begin with at least two as, and end with at least two bs.