在条件状语中，用一般时代替将来时
主要连接词：
if / unless
例如：
Children should not be taken into the room of a very sick person ______ there is some special reason for it.
A.except B. besides C. unlessD.whereas
解题思路：根据上面说过的连接原则，这里必须是一个连接词，而A，B都是介词，因此正确答案只能在C，D中选。whereas意为而，故正确答案为C.
provided / on condition that 知道这也是连接词就可以了，一般说，当考题中出现这种词时，应倾向选择。
3) 原因状语从句：
主要连接词：because/ since / as
要点：不要把连接词 because与介词短语because of 相混淆;
不要把表示原因的since与表示时间的since自从相混淆;
不要把表示原因的as与表示时间的as随着相混淆;
顺便提一下， because表示直接因果关系，而since, as 是对事实的说明，主句和从句之间并不一定具有因果关系.
例如：
As you are already 18 years old, you should know what to do and what not to do.
这个句子用because连接就不太合适。
for 注意：一般只能放在主句后面，即主句 + for从句，例如：
He must have gone to bed, for it is too late. 该句不能用because
now that / seeing that / considering that
Seeing that this problem was settled, they proceeded to the next one.
in that一般放在主句后面，例如：
Humans are superior to animals in that they can use languages as a tool to communicate.