Given:<br /> <img src="https://nimg.ppkao.com/2018-08/longzhengxuan/2018080115582854442.jpg?sign=29e7fb84cc434c87f14e6c00a5e81fa3&t=62d07d42" /><br /> 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");

H、sb1.append("abc"); s1 = s1 + s1.concat("abc");

I、sb1.concat("abc"); s1 = s1 + s1.concat("abc");