String s="abcdedcba";则s.substring（3，4)返回的字符串是以下选项中的哪个（)。

A.int i=s.length();

B.s[3]=”x”;

C.String short_s=s.trim();

D.String t=”root”+s;

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

String s = new String(xyz);创建了几个String Object

A.String s1=”abc”; String s2=”abc”;则s1= =s2

B.String[] s=”abc”;

C.new String s=”abc”;

D.String s=new String(“abc”);

A.String s="你好";int i=3; s+=i;

B.String s="你好";int i=3; if(i==s){ s+=i};

C.String s="你好";int i=3; s=i+s;

D.String s="你好";int i=3; s=i+;

String s = new String("xyz");创建了几个String Object？

二者之间有什么区别？

A.getParameter(String s)

B.getValue(String s)

C.getParameterNames(String s)

D.getParameterValue(String s)

下面的哪些程序段可能导致错误？ () Ⅰ: String s = "Gone with the wind"; String t = "good "; String k = s + t; Ⅱ: String s = "Gone with the wind"; String t; t = s[3] + "one"; Ⅲ: String s = "Gone with the wind"; String standard = s.toUpperCase(); Ⅳ: String s = "home directory"; String t = s-"directory":

A．Ⅱ、Ⅲ

B．Ⅱ、Ⅳ

C．Ⅰ、Ⅳ

D．Ⅲ、Ⅳ