2016屆高考英語特殊句式復習
a.otherwise b.if not c.but for that d.if so
（2）虛擬條件句中,含助動詞、情態動詞、動詞be或have等,若將它們提到句首,則需省略if。
should it rain tomorrow, we would have to put off the visit till next week.
（3）在as(so)... as..., than引導的比較狀語從句中。
i know you can do better than peter.
this car doesn't run as fast as that one.
（4）在as引導的讓步狀語從句中，當作表語的單數名詞提前時，不定冠詞要省略。
child as he is, he knows a lot.
4、動詞不定式中的省略
1）有些動詞，如believe, find, think, feel, consider, imagine, prove等后作賓補的結構to be + n./ adj. 中的to be可以省略。
i consider him stupid.
his mother found him a clever boy.
2） 感官動詞see, hear, feel, watch, notice 等以及使役動詞let, make, have后作賓補的動詞不定式中的不定式符號to要省略，但變為被動結構時，to必須保留。
they made the boy go to bed early.
the boy was made to go to bed early.
3) 動詞不定式在prefer，refuse，decide, mean, intend, try，promise, like, love， care，want，hope，wish，expect等動詞后作賓語時，為了避免重復,常承前省略不定式后的內容,但要保留不定式符號 to。
i have asked her to come，but she does not want to.
注意：want，like用在 when，if, what，as 引導的從句中，其后的to也常可省略。
i've decided to do what i like.
i'll teach you if you like.
4）在can not but, can not choose but, can do nothing but..., can't help but..., prefer to do rather than do..., would do... rather than... 之后的動詞不定式一般不帶to；but之前有實義動詞do的某個形式do, does, did, done 而且其賓語是something，nothing，anything和everything等不定代詞時，也不帶to, 否則要帶to。
we have nothing to do now but wait.
i can not but admire his courage.
he has no choice but to accept the fact.
5）在并列結構中為了避免重復，后一個to省略。
i'm really puzzled what to think or say.
但兩個不定式有對照或對比的意義時，則后一個to不能省略。
i came not to scold but to praise you.
6）在why, why not 引導的特殊問句中后跟省略to的動詞不定式。
why talk so much about it? why not try it again?
7）動詞不定式與be able to，be going to，have to，ought to，used to等構成復合謂語時，不定式結構常可省略，但要保留不定式符號to。
i don’t want to wait for him， but l have to.
—why didn’t you come to our party？
—i was going to，but l had a report to write.
8）動詞不定式中動詞原形部分是否省略，主要看句子前面是否已出現過同樣的動詞。如果句子前面出現過同樣的動詞，為了避免重復，句子后面的不定式常省略動詞原形，而保留不定式符號to。
don't go till i tell you to.
9）動詞不定式在ask，warn，tell，advise，force，wish，expect，allow，permit , invite, persuade, order, would like, forbid等動詞后作賓語補足語或主語補足語時，常可省略。