下面的哪一个程序片断可能导致错误。 (    )

A.

  String s = "Gone with the wind";

  String t = " good ";

  String k = s + t;

B.

  String s = "Gone with the wind";

  String t;

  t = s[3] + "one";

C.

  String s = "Gone with the wind";

  String standard = s.toUpperCase();

D.

  String s = "home directory";

  s = s + "directory";

这个题怎么做呀？

下面的哪一个程序片断可能导致错误。 (    )

A.

  String s = "Gone with the wind";

  String t = " good ";

  String k = s + t;

B.

  String s = "Gone with the wind";

  String t;

  t = s[3] + "one";

C.

  String s = "Gone with the wind";

  String standard = s.toUpperCase();

D.

  String s = "home directory";

  s = s + "directory";

这个题怎么做呀？