g for sightseeing.
My idea is that we (should) do exercises first.
在feel, hear, notice, observe, see, watch, have, let, make等词后的补足语中,不定式不带to。但是这些句子如果变成被动结构时,就必须带to。例如：I often hear him sing the song.
He is often heard to sing the song.
注意：不定式动词在介词but, except, besides后面时,如果这些介词之前有行为动词do的各种形式,那么,这些介词后的不定式不带to,否则要带to.如：
She could do nothing but cry.
What do you like to do besides swim?
I have no choice but to go.
作定语的不定式如果是不及物动词,或者不定式所修饰的名词或代词是不定式动作的地点、工具等,不定式后面须有相应的介词。例如：He is looking for a room to live in.
There is nothing to worry about.
Please give me a knife to cut with.
There / It is no use/ good/ not any use/ good/ useless doing sth.
admit,appreciate, avoid, consider, delay, enjoy, escape, excuse, feel like, finish, forgive, give up, imagine, include, keep, mention,mind,miss,practise, put off, resist, risk, suggest, can’t help, can’t stand(无法忍受)等。
I tried not to go there.(我设法不去那里。)
I tried doing it again.(我试着又干了一次。)]
mean to do 有意... mean doing意味着...
I mean to come early today.(我打算今天早些来。)
Missing the train means waiting for another hour.
allow, advise, forbid, permit
We don’t allow smoking here. We don’t allow students to smoke.
The window needs(requires, wants)cleaning(to be cleaned).
在短语devote to, look forward to, pay attention to, stick to, be used to, object to,thank you for, excuse me for 等后的动词也必须用动名词形式：I look forward to hearing from you soon.
Badly polluted, the water cannot be drunk.(原因)
Being written in haste, the composition is full of mistakes.
Having been deserted by his guide, he couldn’t find his way through the jungle.(为了强调已完成的动作)
Asked to stay, I couldn’t very well refuse.
这里 asked 可能意味着 having been asked, 也可能意味着when/since I was asked, 但用了 having been asked 就不会有歧义。
Covered with confusion, I left the room.我很窘地离开了房间。
United, we stand; divided, we fall. 团结则存，分裂则亡。
He used to live in London, use(d)n’t he /didn’t he?
There used to be a cinema here before the war, use(d)n’t there /didn’t there?
Such things ought not to be allowed, ought they?
He ought to be punished, oughtn’t he?
但在正式文体中,用ought we not形式。例如:
We ought to go, ought we not?或We ought to go ,should we not?
含有情态动词must的句子表示推则,作“想必”解时,疑问部分不可用mustn’t。若前句强调对现在情况的推测,疑问部分用aren’t(isn’t)十主语,例如：You must be tired,aren’t you?若陈述部分的must表示“有必要”时,附加疑问句部分则用needn’t。例如：You must go home right now, needn’t you?
You mustn’t walk on grass, must you?
前句谓语动词是must have＋过去分词时,若前句强调对过去情况的推测(一般有过去时间状语),疑问部分的谓语动词用didn’t＋主语;若前句强调动作的完成,疑问部分的谓语动词用haven’t(hasn’t)＋主语, 例如：
He must have met her yesterday, didn’t he?
You must have seen the film, haven’t you?
陈述句谓语部分出现否定词缀时(前缀或后缀),疑问部分仍用否定结构。例如:He is unfit for his office, isn’t he?
如果陈述部分包含有no, never, hardly, seldom, few, little,nowhere, nothing等否定或半否定词时,疑问部分用肯定形式。例如：He is hardly 14 years old,is he?
Everyone knows his job, doesn’t he?
Everyone knows their job,don’t they?
No one was hurt,were they?
I’m late, aren’t I?
One can’t be too careful,can one(you)?
Have a cup of tea, will you?
Let’s go there,shall we? Let us go there,will you?
同位语从句跟在名词后面,进一步说明该名词的具体内容。引导同位语从句的名词主要有fact, news, promise, idea, truth等。连接词用that (不用which)及连接副词how, when, where, why等。例如：
His delay is due to the fact that the car went wrong halfway.
The news that our team has won the match is true.
She asked the reason why there was a delay.
The question is whether the film is worth seeing.
The news whether our team has won the match is unknown.
Whether we shall attend the meeting hasn’t been decided yet.
It hasn’t been decided whether(if)we shall attend the meeting.
It all depends (on) whether they will support us.
He doesn’t know whether to stay or not.
E)后面紧接or not 时。
We didn’t know whether or not she was ready.
Whether you like it or not, you must do it well.
G)用if会引起歧义时。例如：Please let me know if you like it.
1)先行词是不定代词：all,few,little, much,something,nothing,anything等。All that we have to do is to practise every day.
The first lesson that I learned will never be forgotten.
3)先行词被all,any,every, each, few,little,no,some, 等修饰。
I have read all the book (that) you gave me.
4)先行词被 the only, the very, the same, the last 修饰时。
He is the only person that I want to talk to.
5)先行词既有人又有物时。They talked of things and persons that they remembered in the school.