worth，worthy，worth-while都為adj. 意為"值得"。
1. worth： be worth + n. 當名詞為金錢時，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。