Need it solved in less than 20 minutes. Please let me know how you arrived at the answer.

11. (2 pts) Which of the following sets is not regular? That is, it does not denote the language of a finite state automaton or regular expression. {(ab)" | n >0} | |{a"}}" | n > 0,m>0} {a"b2n|n>0} {b(ab)"bn>0}