1. be（am/is/are/was/were/been）

The small animals are kept in the cages.

He is giving a lecture.

The Internet has too much information that has not been evaluated for accuracy.

Your house is bigger and nicer than mine.

I am to go abroad on business tomorrow.

Tip:

1） be作为本动词表示状态或客观存在等意思。

2） be +不定词连用, 表示约定、义务、命令等未来的动作或状态。

3） be +现在分词构成各种进行时态。

4） be +过去分词构成被动语态。

5） be用于have/has/had后构成完成时。

2. do（does/did）

He didn't find any useful information on the Internet.

These kinds of errors do not occur as often when people use traditional reference materials.

Then, why does he come here?

You do know a lot about computers.

Never did I see such a strange man.

Tip:

1) do作为助动词时的时态、人称和数的变化有do, does, did三种形式。

2) do+主词+原形动词构成疑问句。

3) do+not+原形动词构成否定句。

4) do(+not)+主词用于附带问句。

5) do +原形动词用于加强语气句。

6) Never (Only) 等+do+主词+原形动词用于倒装句

3. have（has/had）

I have never seen such a strange man.

Can I have my hair cut now?

I often have my assistant help me do it.

Tip:

1) 助动词have+过去分词构成完成时态。

2) have +受词+过去分词表示请或让别人做某事。

3) have +受词+原形不定词表示请或让某人做某事。

4. modals（shall/should/will/would/can/ could/may/might/must/need/dare）

Ok, I shall do what you said.

I shall never do such a thing.

You shall give me a cigarette, or I shall tell the boss.

Where shall I meet you?

You should work harder.

You must put on more clothes in case you should catch a cold.

Will you give me a cigarette?

This will be what you need.

She will stand there sleeping for hours.