请教语法题一道

Fibers of hair and wool are not continuous and must normally be spun into thread ____ woven into textile fabrics.

a   as are they
b   when to be
c   that they are
d   if they are to be

答案是D， 为什么B不对，我认为B是状语从句省略了主谓语they are. 而答案D也符合状语从句省略的条件，能不能变成 if to be呢？那岂不是和B没有区别了？状语从句的省略真让人头痛。

B is not correct.

In when 状语从句, 主谓语they are 是不能省略的. I did not see sentence like"sth.. when to be..."

However, "when to.." seems OK.

to be discussed...

偶个人觉得是这样的,状语从句在不产生歧意的时候才能做省略处理,如果会产生歧意,则不能根据语法规则来做出省略处理. 再回头来看B和D. 原本B和D都看似正确,只不过一个是省略句,一个是完整的状语从句罢了~~但省略句的那句省略掉的主语倒底是复数的Fibers还是单数的THREAD??句子的意思会模糊~~所以选了D

还在迷糊中。4楼smile的说法值得商榷。状语从句的省略的条件是严格的，不会引起歧义，省略从句主语的必然是与主句的主语一致，也就是Fibers。若从句主语指的是thread,就决不能省略，但从句主语应该是it,而不是D--if they are to be

这道题是新东方的光盘“高分语法”模拟练习36-14，解释的不清楚，据说都是真题来着，不应该有两个都正确的答案。

ah~~~~~~~~~~偶又想到一个理由哦~~这个还是蛮充分的~~

Fibers of hair and wool are not continuous and must normally be spun into thread ____ woven into textile fabrics.
b   when to be 当...的时候 即使状语从语用了TO BE表示将来时,但是TO BE是计划立刻去做的~~时间上是来不及的~~
d   if they are to be而用了IF语意上就好很多啊~~