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。