worth，worthy，worth-while都为adj.意为"值得"。

1. worth： be worth + n. 当名词为金钱时，表示"…… 值得……"

be worth doing sth."……某事值得被做"

The question is not worth discussing again and again.

2. worthy：be worthy of +n.当名词为抽象名词时表示"……值得……"

be worthy to be done "某事值得被做"

The question is not worthy to be discussed againand again.

3. worth-while： be worth-while to do sth "值得做某事"

worth while： It is worth while doing sth

It is worth while sb to do sth.

例题：

It is not ____ to discuss the question again and again.

A.worth；B.worthy；C.worth-while；D.worth while；

答案：C。

解析：由worth的用法可知，此句只适合词组be worth-while to do sth.。因此选C。