下面的哪些程序片段可能导致编译错误?() 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"; String t=s - "directory";