2．though既指事实，又指设想。可用于句首、句中或句末。
Though he is poor, he is happy.
他虽然穷，但很快乐。
I haven't checked the information yet, though I thik it is correct.
我还没有核实这份资料，但我认为它错不了。
My house, though it is large, is also made of stone and wood.
我的房子虽然大，但是也是用石头和木料搭成的。
提示：
有时though= and yet但是，然而，放在句子末尾，前面用逗号。
It was hard work; I enjoyed it, though.
那工作很苦，但是我喜欢干。
(= It was hard work, but I enjoyed it.)
让步状语从句表示在某种相反的条件下，主句中的情况依然会出现。让步状语从句由although, though, however, whatever, whoever, whomever, whichever, whenever, wherever, whether(是否), no matter (who, what, etc), even if, even though等词引导。
A．although, though
这两个词意思一样，都解释虽然，尽管。although比though正式。
1．although指事实，多用于句首。多数情况下可与though换用。
Although he is young, he is very clever.
他尽管年轻，但很聪明。
Although his illness had prevented him from studying, he managed to pas the exam.
尽管病情妨碍了他学习，但他还是通过了考试。
It was an exciting game, although no goals were scored.
那是一场精彩的球赛，尽管一个球都没进。(although也可放在主句之后)
比较状语从句由as, than引导。
A．as...as, the same as
用于同等程度级的比较。否定句用not so/as …as, not the same …as。
Our country is as big as the whole of Europe.
我们的国同整个欧洲一样大。
The result was not as/so good as I had expected.
结果不如我预料的那么好。
She works in the same building as my sister.
她和我的妹妹在同一大楼上班。
B．than
than表示不同程度级的比较
It rains more often in Shanghai than in Beijing.
上海下的雨比北京的多。
He is two inches taller than his father.
= He is taller than his father by two inches.
他比他爸爸高两英寸。
注意：
在比较从句中通常把和主句重复的部分省掉，如果把省略部分补上，而显得累赘或不合乎习惯。
Lily isn't so clever a girl as Lucy is.
莉莉是一个不如露西那样聪明的女孩。(如说成：Lily isn't so clever a girl as Lucy is clever 显得累赘)
The child sang as sweetly as a nightingale.
这孩子歌唱得同夜莺般婉转。
C．the more..., the more...
这是表示比例的比较，意思是越……就越……。第一个the more 也可以看成是一个条件。
The more you read, the better you understand.
你看的书越多，你懂得就越多。(= If you read more, you will understand better.)
The busier he is, the happier he feels.
他越忙越开心。
The more difficult the questions are, the less likely I am to be able to answer them.
问题越困难，我就越可能回答。
必背：
一些常见的倍数比较句型。
His father is double twice his age.
他爸爸的年龄是他的两倍。
His father is twice double as old as he (is).
Our new school is three times bigger than the old one.
我们的新学校比老学校大三倍。
Our new school is four times as big as the old ne.
我们的新学校是老学校的四倍大。
Our new school is four times the size of the old one.
我们的新学校是老学校的四倍。
方式状语从句是描述动作方式的从句。方式状语从句常由as, as if as though等词引导，通常位于主句之。
A． as, just as
这两个连词的意思是如……，正如……一样。just as 比as 语气要强一些。
Do in Rome as the Romans do.
入乡随俗。
Leave things as they are.
让一切顺其自然。
Please do as you are told.
请按照人家告诉你做的去做。(也可说Please do as told.)
Balloons float in the air just as boats do on the sea.
气球在空中就如同船浮在海面上一样。
在口语中，还可用like来代替as，引导一个方式状语从句。
She is doing the work exactly like I want her to.
她正在完全按照我要她的那样在做这项工作。
Do you make bread like you make cakes
你做面包的方法是不是和做点心一样？
B．as if, as though
由as if 或as though引导的状语从句可以用陈述语气表示可能符合事实的情况，也可以用虚拟语气的过去式表示现在不符的或与事实相反的情况(见第3章虚拟语气)。
She looks as if she is ill.
看上去她好象是生病了。
The boy plays piano as though he has a natural ear for music.
这孩子弹起钢琴来家好象天生很懂音乐似的。
They talked loudly as if nobody were around.
他们大声说话仿佛周围没人似的。
He acted as if/though nothing had happened
他装得似乎什么事也未发生过。
4．unless能作为介词使用，相当于except，而if…not不可以。
Nothing will come out of it unless disaster.
这种事除非引起灾祸之外不会有什么结果。
C．so long as, as long as, on condition that
这几个短语意思差不多，都表示只要，条件是……。
As/So long as we don't lose heart, we'll find a way to overcome the difficulty.
只要我们灰心，我们就能找到克服困难的方法。
You may use the room on condition that so long as you clean it afterwards.
只要你用完后打扫干净，你就可以使用这个房间。
D．in case
in case 既引导目的状语从句，也可以引导条件状语从句，等于if it happens that。
In case I forget, please remind me of my promise.
如果我忘了，请提醒我所做的承诺。
Send s a message in case you have any difficulty.
万一你有什么困难，请给我们一个信儿。
E．providing, provided that, supposing, suppose that, given that
这几个短语意思相近，有如果，只要，假如等意思。
Given that they are inexperienced, they've done a good job.
考虑到他们缺乏经验，他们的工作已做得很好了。(that可以省略)
provided Providing(that)we invite him, he would surely come to dinner.
假如我们邀请他的话，他肯定会来吃饭的。
Suppose/Supposing we can't get enough food, what shall we do
假设我们弄不到足够的食物，那我们怎幺办？(仅用于疑问句)
3．unless引导的状语从句可用否定结构，而if…not引导的从句不可再用否定结构。
Don't ask me to explain again unless you really don't understand.
不要再叫我解释了，除非你真的不懂。
2．如果主句描述的是情感或情绪活动方面的内容，if…not结构不能换成unless。如：
I'll be quite glad if she doesn't come this evening.
她今晚如果不来我很高兴。
条件状语从句是表示主句动作发生的前提或条件的从句。条件状语从句分为真实条件状语从句和非真实条件状语从句(见第3章)。引导条件状语从句的有if, unless, so as long as, as so far as, on condition that, in case, suppose, supposing等。条件状语从句中的谓语动词一般要用现在时或过去时代替一般将来时或过去将来时。
A．if if表示正面条件，意为如果。
If you ask him, he will help you.
如果你向他请求，他会帮助你。
Difficulties are nothing if we are not afraid of them.
如果我们不怕困难，困难就算不了什么了。
If I do not understand what he says, I always ask him.
我不懂他的话时, 总是去问他。(if = when)
比较：
if only和only if的对比。
if only 解释但愿，要是??就好了，表示一个不可能实现愿望，要用虚拟语气。
only if 解释只有，等于only on condition that，从句用陈述语气。
Only if you heat ice, it turns to water.
只有当你给冰加热，它才会变成水。
If only I knew!
要是我知道该多好。
B．unless
unless = if not, 表示反面条件，意思是如果不、除非。
They will go tomorrow unless it rains.
除非明天下雨，否则他们会去的。
(They will go tomorrow if it doesn't rain.)
I won't let you in unless you show me your pass.
如果你不出示通行证，我就不让你进来。
(= I won't let you in if you don't show me your pass. )
if...not和unless通常是可以换用的。但在下列情况下，两者是有区别的：
1．unless多引导真实条件句，if…not可以引导真实条件句或非真实条件句。
He won't be able to pass the final exams unless he works hard.
除非他努力，否则就通过不了期末考试。
He won't be able to pass the final exams if he doesn't work hard.
如果他不努力，就通过不了期末考试。
He would pass the final exams if he worked hard.
要是他努力的话，他就会通过考试。(非真实条件句。含义是He doesn't work hard.)
3．such + 形容词 + 不可数名词 + that-从句
He made such rapid progress that the teacher praised him.
他的进步很快，老师表扬了他。
H shut the window with such force that the glass broke.
他关窗子用了那么大的劲，玻璃都碎了。
提示：such+a/an+形容词+单数名词结构可以和so +形容词+a/an+单数名词结构互换。
He told us such a funny story that we all laughed.
→ He told us so funny a story that we all laughed.
他给我们讲了一个如此有趣的故事，大家都笑。
→The story he told us was so funny that we all laughed.
他给我们讲的故事是如此有趣，大家都笑了。
E． such that
such that可以连用，意思是(是)这样...以致。
Mother's answer was such that she didn't say yes and she didn't say no.
妈妈的回答就是这样，既没有同意也没有不同意。
His anger was such that he lost control of himself.
他勃大怒，以致不能自制。
比较：such ...that ... 引导的是结果状语从句。
such ...as ...引导的是定语从句(请参考第10章定语从句)。
She had such a fright that she fainted.
她吓得昏了过去。
Luckily such earthquakes as can cause a lot of damage do no happen very often.
很幸运，这种破坏性很大的地震并不经常发生。(关系代词as在定语从句中作主语)
2．such + 形容词 +复数名词+ that-从句
He gave such important reasons that he was excused.
他说出了这么重要的理由，得到大家的谅解。
They are such interesting novels that all of us want to read them.
这些是十分有意思的小说，大家都想看。