A regular expression whose language is the reversal of the language of this regular expression: 1*23*. Recall that the reversal of a language is formed by reversing all its strings, and the reversal of a string a1a2...an is an...a2a1.

a) 3*1*2

b) 1*3*2

c) 3*21*

d) 21*3*

Please explain me