主 +系 +形容词后能加 什么?后面的 做什么成分 如：the book is worth reading.readin

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.
ps：至於reading做什么 我不太清楚,be worth doing 是一种固定搭配