英语五级写作语法指导
原因解释型
1. 给出一个事实，要求解释它的原因。
陈述这个事实 As is know by all， ……
Among countless factors which contribute to XXX， there exist three most conspicuous ones：
One of the primary causes is that…
XXX also results from…
… is responsible for xxx， as well.
To put all into a nutshell， I draw the conclusion that A，B and C are three main contributors to XXX
2. What should we do? How do something influence our lives? what are the characters of something.
背景描述
There are numerous approaches to solving…/impacts on sth. /characteristics of… ， and I would explore the most conspicuous ones there.
One of the primary method， to my mind， is that…
one of the primary impact， to my mind， is that…
one of the primary characteristic， to my mind， is that…
a more subtle point which we must consider is that…
In addition/ furthermore ……
In conclusion， Taking into account of all these methods/ affects / aspects， we may reach the conclusion that……
混合条件句
主句与从句的动作发生在不同的时间，这时主，从句谓语动词的`虚拟语气形式因时间不同而不同，这叫做混合条件句。
If you had asked him yesterday, you would know what to do now.
(从句与过去事实相反，主句与现在事实相反。)
If it had rained last night (过去), it would be very cold today (现在).
情态动词的语法特征
1) 情态动词不能表示正在发生或已经发生的事情，只表示期待或估计某事的发生。
2) 情态动词除ought和have外，后面只能接不带to的不定式。
3) 情态动词没有人称，数的变化，即情态动词第三人称单数不加-s。
4) 情态动词没有非谓语形式，即没有不定式，分词，等形式。
比较can和be able to
1)can、could表示能力;可能(过去时用could), 只用于现在式和过去式(could)。be able to可以用于各种时态。They will be able to tell you the news soon.他很快就能告诉你消息了。
2)只用be able to
a. 位于助动词后。
b. 情态动词后。
c. 表示过去某时刻动作时。
d. 用于句首表示条件。
e. 表示成功地做了某事时，只能用was/were able to，不能用could。
He was able to flee Europe before the war broke out.
= He managed to flee Europe before the war broke out.
注意：could不表示时态
1)提出委婉的请求，(注意在回答中不可用could)。
-- Could I have the television on?
-- Yes, you can. / No, you can’t.
2)在否定，疑问句中表示推测或怀疑。
He couldn’t be a bad man.
他不大可能是坏人。
比较may和might
1)表示允许或请求;表示没有把握的推测;may放在句首，表示祝愿。
May God bless you!
He might be at home.
注意：might表示推测时，不表示时态。只是可能性比may小
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