6.2 worth 的用法
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worth，worthy，worth-while都為adj.　意為"值得"。
1. worth： be worth + n.　 當(dāng)名詞為金錢時(shí)，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(shí)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.
　　-while　 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。