For $$\sum = \left\{a, b\right\}$$ the regular expression $$r = (aa) * (bb) * b$$ denotes

A

Set of strings with 2 a’s and 2 b’s

B

Set of strings with 2 a’s 2 b’s followed by b

C

Set of strings with 2 a’s followed by b’s which is a multiple of 3

D

Set of strings with even number of a’s followed by odd number of b’s