In linux regex, when "?" is used then it will be the case that preceding character matches 0 or 1 times.
when "*" is used then preceding character matches 0 or more times.
Hence for a? = a will be appear 0 or 1 time only.
b*? = b will be appear 0 or more times.
Hence a?b*? = epsilon, b,bb,bbb,.... , ab,abb,abbb...
Hence answer is option C.