Choose the appropriate regular expression for the following grammar:

S$->$ aQobQo

Qo$->$ CQoQ$1$

Q$1$aQ$1$bQ$2|1$

Q$2->$ CQ$21$

No such regular expression exists; this is not an s$-$grammar.

$($a$+$b$)$ca$*(1+$ bc$*)$

$($a$+$b$)($c$*+($a$^2+$ b$))$c$*$

abc$*($a $+$ b$)$c$*$