Java SCJP 多型与转型

有下列程式：

class ClassA{}
class ClassB extends ClassA{}
class ClassC extends ClassA{}
public class Test{
public static void main(String[] args){
ClassA p0 = new ClassA();
ClassB p1 = new ClassB();
ClassC p2 = new ClassC();
ClassA p3 = new ClassB();
ClassA p4 = new ClassC();
}
}

下列程式何者正确？(请勾选出三项)
( )A. p0 = p1;
( )B. p1 = p2;
( )C. p2 = p4;
( )D. p2 = (ClassC)p1;
( )E. p1 = (ClassB)p3;
( )F. p2 = (ClassC)p4;

答案：A、E、F

起初做这题的时候，竟然把它看成是比较了，所以很简单的题目，我就错了！