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?
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