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