21.1 一般疑问句
含 be 动词：
Are you ready?
你准备好了吗？含情态动词：
Can you swim?
你会游泳吗？含实义动词，需要助动词 do/does/did：
Do you like coffee?
你喜欢咖啡吗？
Does she speak English?
她说英语吗？
Did they arrive yesterday?
他们昨天到了吗？注意：用了 does/did 后，实义动词用原形。
错误：Does she likes English?
正确：Does she like English?21.2 特殊疑问句
结构：
疑问词 + 一般疑问句语序例句：
Where do you live?
你住在哪里？
Why did he leave?
他为什么离开？
How can I improve my writing?
我如何提高写作？当疑问词本身作主语时，不需要助动词倒装：
Who called you?
谁给你打电话了？
What happened?
发生了什么？21.3 否定句
be 动词后加 not：
He is not tired.情态动词后加 not：
You should not do that.实义动词借助 do/does/did not：
I don't know.
She doesn't like fish.
They didn't come.21.4 祈使句
祈使句用于命令、请求、建议。
Open the door.
请开门。
Please sit down.
请坐。
Don't be late.
不要迟到。委婉表达：
Could you open the window?
你能打开窗户吗？
Would you mind closing the door?
你介意关门吗？