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：
选项：

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;; H:s3 = s1 # s2;