请教大家！

[dulang200x]

Q50
Given the following interface definition, which definitions are valid?

interface I {
void setValue(int val);
int getValue();
}

DEFINITION A:
(a) class A extends I {
int value;
void setValue(int val) { value = val; }
int getValue() { return value; }
}

DEFINITION B:
(b) interface B extends I {
void increment();
}

DEFINITION C:
(c) abstract class C implements I {
int getValue() { return 0; }
abstract void increment();
}

DEFINITION D:
(d) interface D implements I {
void increment();
}

DEFINITION E:
(e) class E implements I {
int value;
public void setValue(int val) { value = val; }
}

1) Definition A.
2) Definition B.
3) Definition C.
4) Definition D.
5) Definition E.
答案是2，3
我认为是1，2，3
Definition A中，A继承了B，且把B中的所有abstract都实现了，不是对的吗？

[dulang200x]

Q51
Which statements concerning the methods notify() and notifyAll() are true?

1) Instances of class Thread have a method called notify().
2) A call to the method notify() will wake the thread that currently owns the monitor of the object.
3) The method notify() is synchronized.
4) The method notifyAll() is defined in class Thread.
5) When there is more than one thread waiting to obtain the monitor of an object, there is no way to be sure which thread will be notified by the notify() method.

不好意思，还有一题！我认为选1，2，3，5
答案是1，5
请帮忙解释下，2，3 为什么不对？

[BenLLLL]

a中的class 不能extends 接口，要implements