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

Given:

22. StringBuilder sb1 = new StringBuilder(“123”);
23. String s1 = “123”;
24. // insert code here
25. System.out.println(sb1 + ” ” + s1);

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”);