ANS:C -

I don't know much about this. But i think in standard form, maxterms are used. In the question, there are 8 possible combinations for answer D and 2 possible combinations for answer A. Answer C is standard because it contains max terms only(maxterms are terms which includes are variables within the expression).

Eg: (A+B')(A'+B+C') = (A+B'+C)(A+B'+C')(A'+B+C')