下列关于接口的说法不正确的是（ ）。

A．String s = "hello"；String t = "good"；String k = s + t;
B．String s = "hello"；String t;t = s[3] + "one"；
C．String s = " hello "；String standard = s.toUpperCase( )；
D．String s = "hello"；String t = s + "good"；

A．package testpackage；public class Test{ }
B．import java.io.* ；package testpackage；public class Test{ }
C．import java.io.*； class Person{ }public class Test{ }
D．import java.io.*；import java.awt.*；public class Test{ }