186. weather, if　　

当“是否”解时，只有在宾语从句中二者可以互换，其余都用weather；例：I don't know if/whether he will come.
当“如果”解时用if 例：If he comes, I'll let you know.

187. and, or　　

and并且；例：Hurry up and you'll catch the bus.
or或者，否则，常用于否定句中 例：Hurry up or you'll miss the bus.

188. because, since, as, for　　

原因由强到弱为：because, since/as, for. 在句中的位置如下：1)…because… 2) Since/as…, … 3) …, for…

例：Since I was ill, I didn't go.

189. when, as, while (表时间)　　

when从句动词点动词，持续性动词均可；
as重在表示动作同时发生，伴随进行；
while从句动词为持续性动词 例：While I slept, a thief broke in.

190. the same…as, the same…that　　

the same…as和…一样的（相似但不同一）；
the same…that 同一物体 例：This is the same pen that I used yesterday. (同一支笔)