原因解釋型
1. 給出一個事實，要求解釋它的原因。
陳述這個事實 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……
混合條件句
主句與從句的動作發生在不同的時間，這時主，從句謂語動詞的虛擬語氣形式因時間不同而不同，這叫做混合條件句。
If you had asked him yesterday, you would know what to do now.
(從句與過去事實相反，主句與現在事實相反。)
If it had rained last night (過去), it would be very cold today (現在).
情態動詞的語法特徵
1) 情態動詞不能表示正在發生或已經發生的.事情，只表示期待或估計某事的發生。
2) 情態動詞除ought和have外，後面只能接不帶to的不定式。
3) 情態動詞沒有人稱，數的變化，即情態動詞第三人稱單數不加-s。
4) 情態動詞沒有非謂語形式，即沒有不定式，分詞，等形式。
比較can和be able to
1)can、could表示能力;可能(過去時用could), 只用於現在式和過去式(could)。be able to可以用於各種時態。They will be able to tell you the news soon.他很快就能告訴你訊息了。
2)只用be able to
a. 位於助動詞後。
b. 情態動詞後。
c. 表示過去某時刻動作時。
d. 用於句首表示條件。
e. 表示成功地做了某事時，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不表示時態
1)提出委婉的請求，(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，疑問句中表示推測或懷疑。
He couldn’t be a bad man.
他不大可能是壞人。
比較may和might
1)表示允許或請求;表示沒有把握的推測;may放在句首，表示祝願。
May God bless you!
He might be at home.
注意：might表示推測時，不表示時態。只是可能性比may小
