To be 的用法

Question

什么时候用它？不懂……

Answer 1

To be 的用法可以写一本书。

To be 是不规则动词，你必须熟练掌握它的各种形式：
am , is , are , was , were , is being , has been , should be , could be , would be , might be , shall be , will be , can be , must be , need to be ...
轻易得到的东西你不会珍惜，所以我就不多说了。

它的用途主要有：
1. 系动词，相当于“是”
例如：The flower is red .
2. 表存在，
例如：China is in Asia .
3. 表判断（是/否），
例如：Are you there ? Yes , I am .

在学习过程中，你还会发现它的许多用法。对 to be 的掌握程度（不仅仅是背下来）是你英语水平的标志之一。

参考资料：http://hi.baidu.com/crania

Answer 2

殊疑问句结构：特殊疑问词＋to be＋主语＋其它成分。

What is your name? My name is Tom.

Where are you from? I am from American.

Where are they? They are on the playground.

Who is she? She is my aunt.

Answer 3

if
有两个词义
1.
是否
用于名词性从句
比如i
want
to
know
if
you
can
go
with
me.
2.
如果
用于条件状语从句
if
you
have
any
time,
you
can
help
me
with
my
english
be
going
to
表示将要
后面加动词原形
i
am
going
to
buy
a
book

Answer 4

if
有两个词义
1.
是否
用于名词性从句
比如i
want
to
know
if
you
can
go
with
me.
2.
如果
用于条件状语从句
if
you
have
any
time,
you
can
help
me
with
my
english
be
going
to
表示将要
后面加动词原形
i
am
going
to
buy
a
book