对于以下代码段：String s1 = "a";String s2 = "b";String s3 = "";以下操作可以编译的是：

A、s3 = s1 + s2;;

B、s3 = s1 - s2;;

C、s3 = s1 & s2;;

D、s3 = s1 . s2;;

E、s3 = s1 $ s2;;

F、s3 = s1 ^ s2;;
G:s3 = s1 * s2;