Marcus took half an hour to complete his homework. He started doing his homework at $$11.50 \rm a.m$$. What time did Marcus complete his homework? 
选项为:A:$$11.20 \rm a.m$$.  B:$$11.20 \rm p.m$$.  C:$$12.20 \rm a.m$$.  D:$$12.20 \rm p.m$$.  请回答其中一个选项.