助动词详解
助动词（Auxiliary Verbs）也称为协助动词，包括 be、do、have、will 等动词。它们在句子中用于构成否定句、疑问句、进行时和完成时。
助动词 Be
be 动词既可以用作助动词，也可以用作主要动词。它是一个不规则动词，具有多种形式：
现在式
I am learning English.
He/she/it is reading a book.
We/you/they are playing soccer.
过去式
I/he/she/it was sleeping.
We/you/they were talking.
过去分词
been (used in perfect tenses)
Be 动词用于进行式
现在进行时: She is reading a book.
过去进行时: They were watching TV.
现在完成进行时: He has been working for hours.
Be 动词用于被动式
一般现在/过去时: The car is/was repaired.
现在/过去完成时: The project has/had been completed.
将来时: The meeting will be held tomorrow.
助动词 Have
have 动词可以用作助动词和主要动词，形式如下：
现在式
I/we/you/they have a meeting.
He/she/it has a book.
过去式
They had a great time.
Have 用于完成式
现在完成时: I have finished my homework.
过去完成时: She had visited her friends.
现在完成进行时: They have been studying all night.
助动词 Do
do 动词可以是助动词或主要动词，形式如下：
现在式
I/we/you/they do sports.
He/she/it does homework.
过去式
He did his best.
Do 用于否定句和疑问句
否定句: I do not like coffee.
疑问句: Do you understand the lesson?
助动词 Will
will 是情态助动词，用于一般将来时、将来进行时和条件句：
一般将来时: She will travel to Japan next year.
将来进行时: They will be having dinner at 8 PM.
第一条件句: If it rains, we will stay at home.
注意：在以下情况下，助动词 do 不用于否定或疑问句：
- 主要动词是 be 动词。
- 已经使用了另一个助动词（如 have、be、will）。
- 使用了情态动词（can、could、may 等）。
- 疑问句的问题是在询问主词。