二、条件状语从句
if 好的条件，可用 provided／providing／suppose／supposing(that)/ on condition that 替换
不好的条件可用 so／as long as替换
如：If／Provided(that)it snows tomorrow, we shall play snowballs．
If／So long as it snows tomorrow, we shall delay our trip to the seaside．
练习：
1. We’ll visit Europe next year ______ we have enough money.
A. lest B. until C. unless D. provided
only if／if only
1．only if=only on condition that“只要，只有…”
如：Only if a teacher has given permission is a student allowed to enter this room．(主句例装)
只有得到教师的允许，学生才可以进这间屋。
2．If only“要是…就好了”(虚拟)
如：If only we had arrived in time，we would not have missed the train．
if／unless
unless=if…not (且语气较强)
如：You will make progress if you study hard．
比较：You will never make progress unless you study hard．
Unless he comes，we won’t be able to go．

三、原因状语从句
because／since／as区别(for)
1．because原因语气最强，它引导从句是说话的重心
如：He failed because he was too careless． 因为他太粗心，所以才失败了
2．since=now／seeing／considering(that)“既然”表对方已知晓的无须加以说明的原因或事实。既成事实的原因
如：Seeing everybody is here，let’s begin．
Since you ask，I will tell you．你既然问，我就告诉你
Seeing that it’s raining，you had better stay indoors．因为正在下雨，你最好留在室内。
练习：
1. _______ you are leaving tomorrow, we can eat dinner together tonight.
A. For B. Since C. Before D. While
3．as 往往十分明显的原因，语气较弱
如：As you are in poor health，you should not sit up late．既然你身体不好，你就不应该熬夜。
for 为并列连词, 不可在句首，表补充说明
如：It must have rained last night，for the ground was wet this morning.
not…because 句型(否定转移)“不因……而”
如：You should not despise him because he is poor． 不要因他穷而轻视他。
如：She didn’t marry you because you had money． 不是因为你有钱，她才嫁给你。
because／because of 区别
I couldn’t go to school 我因生病，所以没有去上学。
Because+ 从句
because of + N

五、让步状语从句
1．Though／Although／Even if／Even though/ while he is young，he knows a lot／much．
=Young as／though he is，he knows a lot／much．
=Child as he is，he knows a lot／much．
=In spite of／Despite／With all／For all being a child，he knows much.
=He is young．but he knows a lot／much．(不与but连用)
2．Wh-+ever…．
练习：
1. __________ I admit that the problems are difficult，I don’t agree that they can’t he solved.
A. Suppose B. Because
C. While D. Until
2. ________ little you may like it，old age comes to most of us.
A. So B. Since
C. However D. Despite
3. _______ we have finished the course, we shall start doing more revision work.
A. For now B. Now that C. Ever since D. By now