Please select the correct answer:

The first five questions use alphabet ? = {a, b} and have exactly one correct answer. Recall that superscript plus means "one or more" and that zero counts as an even number. For this and the next two questions, say which prose description goes with the regular expression at top. The first char in a string has index 1, not 0. Regular expression: (a+b)*a+ Select an answer and submit. For keyboard navigation, use the up/down arrow keys to select an answer. a Nonempty strings in which every bis immediately preceded by an a. b Nonempty strings in which every bis immediately preceded and followed by an a. Nonempty strings X such that between every two b's in X there is at least one a. d Strings that alternate ab but can have any positive number of a's on the end. e Strings in which every b is immediately preceded and followed by an a