Correct is B and C, because: - A is Wrong, will print "XXXX-XXXX-XXXX-1234-5678-9101-1121" because String is immutable and in the line 2 of the Anwser is an code isolated, not chance the "sb" variable - B is Correct, you can acess the value of the method substring with the parrametrs direclty - C is Correct, with the method "append" of StringBuilder in the line 2 of the Answer, you can concatenate with an String and can choose the range of String that you want concatenate - D is Wrong, because de range is incorrect

insert(int Index, String) method of StringBuilder replaces only the given index => D wrong

public class Main2 { public static String maskCC(String creditCard){ String x = "XXXX-XXXX-XXXX-"; return x + creditCard.substring(15,19); } public static String maskCC2(String creditCard){ String x = "XXXX-XXXX-XXXX-"; StringBuilder sb = new StringBuilder(x); sb.append(creditCard, 15, 19); return sb.toString(); } public static void main(String[] args) { System.out.println(maskCC("1234-5678-9101-1121")); System.out.println(maskCC2("1234-5678-9101-1121")); } }

Correct Anwser BC. Tested

B and C is the correct answer