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。