worth，worthy，worth-while都為adj.　意為"值得"。
1. worth： be worth + n.　 當(dāng)名詞為金錢時，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.　當(dāng)名詞為抽象名詞時表示"……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.

典型例題
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，此句只適合詞組be worth-while to do sth.。因此選c。