186. weather, if　　

當(dāng)“是否”解時(shí)，只有在賓語(yǔ)從句中二者可以互換，其余都用weather；例：I don't know if/whether he will come.
當(dāng)“如果”解時(shí)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，否則，常用于否定句中 例：Hurry up or you'll miss the bus.

188. because, since, as, for　　

原因由強(qiáng)到弱為：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 (表時(shí)間)　　

when從句動(dòng)詞點(diǎn)動(dòng)詞，持續(xù)性動(dòng)詞均可；
as重在表示動(dòng)作同時(shí)發(fā)生，伴隨進(jìn)行；
while從句動(dòng)詞為持續(xù)性動(dòng)詞 例：While I slept, a thief broke in.

190. the same…as, the same…that　　

the same…as和…一樣的（相似但不同一）；
the same…that 同一物體 例：This is the same pen that I used yesterday. (同一支筆)