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.
典型例题
It is not ____ to discuss the question again and again.
A.worthB.worthyC.worth-whileD.worth while
答案C. 由worth的用法可知，此句只适合词组be worth-while to do sth.。因此选C。