Given:

Which code fragment, inserted at line 24, outputs "123abc 123abc"?（）

A.sb1.append("abc"); s1.append("abc");
B.sb1.append("abc"); s1.concat("abc");
C.sb1.concat("abc"); s1.append("abc");
D.sb1.concat("abc"); s1.concat("abc");
E.sb1.append("abc"); s1 = s1.concat("abc");
F.sb1.concat("abc"); s1 = s1.concat("abc");
G.sb1.append("abc"); s1 = s1 + s1.concat("abc");
H.sb1.concat("abc"); s1 = s1 + s1.concat("abc");