CS 290 Practice with regular expressions b. All strings that contain the substring aa c. All strings that contain the substring aa and the substring bb d. All strings that contain at least one a e. All strings that contain at least one a and at least one b f. All strings that contain either aa or bb, but not both. CS 290 1. Practice with regular expressions For each of the following, give three examples of strings that are members of the language described by the regular expression, and give three examples of strings that are not in the language described by the regular expression. (In all of these cases, use Σ = (a, b).) a. a"b" b. (ab')a c. (b*a)* d. (aub) abba(a U b)* 2. For each of the following languages, find a regular expression that describes its strings. (Use Σ = (a,b).) a. All strings that do not begin with aa