单项选择题
A."I love this game" B."I love this" C."I love" D."I"
A.sum<double,double,double>(d1,d2) ; B.sum<double;double>(d1,d2) ; C.sum<double>(d1,d2) ; D.sum(d1,d2) ;
A.+和= B.=和<< C.==和<< D.=和[]