to后面的动词往往可以省略的,什么时候不可以省略好像是说什么be什么的,可是我忘记了.

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动词不定式中的省略现象可分为两种情况,一是动词不定式符号to后的动词部分的省略；二是动词不定式符号to的省略.
一、省略动词不定式符号to后的动词部分的情况
1.一些表示心理活动、情感态度的动词或短语,如expect \want \hope \wish \love \hate \decide \plan \mean \try \would like \be ready \be afraid \be glad等后,动词不定式省略to后面的动词部分,但保留to.例如：
(1)-I 'll be away on a business trip.Would you mind looking after my dog ?
-Not at all .I 'd be g l ad to.
(2)-Will you go with me ?
-Well ,I 'd like to.
(3)-Will you go home tomorrow?
-No.I 'm going to a lecture,or at least I am planning to.
2.不定式作宾语补足语时,省略to后的动词部分,即用to代替整个不定式.例如：
(1)The boy wanted to ride his bicycle in the street?but his mot her told him not to.
(2)You'd better finish the job on time if he ordered you to.
3.在一些情态动词或助动词ought to \have to \used to \be able to后.例如：
(1)-Must I go now?
-No.You don 't have to.
(2)-Are you planning to see your grandfather ?
-No.But I ought to.
二、省略动词不定式符号to的情况
1.动词不定式作感官动词feel \see \notice \watch \find \hear \listen to \observe和使役动词have \make \let等的宾语补足语时,动词不定式符号to省略.如果这些动词用于被动语态,其后的动词不定式符号to不能省略(但let除外).例如：
(1)We often hear him sing the song at home .
(＝He is often heard to sing the song at home.)
(2)The y knew her very well.They had seen her grow up from childhood.
(＝They knew her very well.She was seen to grow up from childhood.)
注意： get作使、让、叫某人做某事时,要用g e t s b.to do s t h.结构.例如：
Mot her got Tom to buy a pack of sugar.
2.两个或两个以上的动词不定式由连词and \or \than \but连接时,从第二个不定式起,往往省略不定式符号to.但如果强调对比之意时不省略.例如：
(1)She 'd like to take off her coat and have a break.
(2)The students are taught to read,write and do many other things.
(3)I t 's more difficult to do than to say .(强调语意前后对比)
(4)The teacher came not to punish you but to help you.(强调语意前后对比)
(5)I wondered whether to study or to work.(强调语意前后对比)
3.不定式作表语,用来解释主语或主语从句中do的精确含义时,往往可以省略动词不定式符号to.例如：
(1)The first things he did was go up to her trainer and thank her for all her help during her training.
(2)What we want to do now is lie dow