Question

be怎么用啊？怎么样有时候是is are am 有时候又是用be啊？

Answer 1

一，系动词be
be为连系动词，中心词义是"是"，句型为"主+系+表"结构。be的形式常用am, is, are(现在式);was, were(过去式);will/can/may/must be(助动词/情态动词+原形);have/has/had been(助动词+过去分词)等。如：
To help animals is helping people.(一般现在时)
The twins were very busy yesterday.(一般过去时)
It will be sunny tomorrow.(一般将来时)
She has been ill for over a week.(现在完成时)
二，助动词be
助动词be，无词义，辅助主要动词一起在句中作谓语动词。用法如下：
1. be+doing：构成进行时态，有现在和过去两种进行时态。如：
The girls is reading and copying the new words now.
Young Tom was always asking questions and trying out new ideas.
2. be+done：构成被动语态(主语是动作的承受者，done必须是及物动词)。如：
Tea is grown in my hometown.(一般现在时的被动语态)
This building was built three years ago.(一般过去时的被动语态)
Our classroom has been cleaned and tidied already.(现在完成时的被动语态)
How could this kind of cakes be made in your home?(含情态动词的被动语态)
That is a day never to be forgotten.(动词不定式的被动语态)
3. be+going to do，表示"打算或将要做某事"，be有现在和过去两种形式。如：
We are going to plant trees in the park.
I didn't know if she was going to come here.
4. be+to do，表示"按计划安排将要做某事"。如：
The new shop is not to be opened till next Monday.
One night an angel came to Mary and told her that she was to have this special boy.
三，be动词的用法there be句型
there be句式为：there be+主语部分+状语部分，表示"某处存在某物"，be常用现在时，过去时和将来时等。如：
Oh, cool! And there are many things to see. There is even a deer park in Sanya.
There are about 80 pyramids in Egypt.
Will there be a football match in your school next week?
四，实义动词be
可以将be视为实义动词，因为它具有实际的词义，如"成为;做;发生;举行;逗留;到达"等。如：
His daughter wants to be a doctor for animals in her twenties.
Kate's birthday party will be at half past six this evening.
Jim has been in China for more than two years, but he has not yet been to Yichang.
以上be动词的用法的四个功能中，第一个功能最常见，第三个功能是考试的重点也是难点。为了方便大家对Be动词用法的记忆，总结了be动词的用法的常用口诀：我用am，你用are，is连着他，她，它;单数名词用is，复数名词全用are。

Answer 2

根据不同的时态和主语，be可能会被替换为am/is/was/are/were/been/being/be
比如一般现在时：
I am, she/he/it is, you/they are
一般过去时：
I/he/she/it was, you/they were
情态动词后：
will/should/would be
完成时：
I/they have been, I/she/he/they had been
being的用法很杂，很多时态都可能用到。