单选题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"？（）Asb1.append（abc）； s1.append（abc）；Bsb1.append（abc）； s1.concat（abc）；Csb1.concat（abc）； s1.append（abc）；Dsb1.concat（abc）； s1.concat（abc）；Esb1.append（abc）； s1 = s1.concat（abc）；
单选题
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）；
参考解析
解析：
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