Which of the following statements will correctly copy the contents of one string into another?

• String s1 = "String"; String s2; s2 = s1;
• String s1 = "String" ; String s2; s2 = String.Concat(s1, s2);
• String s1 = "String"; String s2; s2 = String.Copy(s1);
• String s1 = "String"; String s2; s2 = s1.Replace();
• String s1 = "String"; String s2; s2 = s2.StringCopy(s1);