4个简单英语句子的语法疑问。

Question

一
Don't let the children stay up too late on weekends, will you?
Don't let the children eat a lot of sweets,shall we?
这组句子后面的附近疑问词为什么会不同？语法书说不是只有let's的时候才用shall we的吗？期待您的解答。

二
She had her hair cut the day before yesterday,didn't she?
You had your watch repaired yesterday,hadn't you?
这2个句子，看不出来结构上有什么不同。为什么它们的附近疑问部分，会不同呢？迷惑……期待您的解答(*^__^*)
三。Why are unit nouns especially useful when they are used to modify a mass noun?
请问这句话中的 unit nouns，以及 mass noun，分别是什么意思？谢谢！

Answer 1

(you) Don't let the children stay up too late on weekends, will you?
这句说话祈使的对象是you，所以用will you

（we） Don't let the children eat a lot of sweets,shall we?
祈使对象是we，包括说话人，所以用shall we

She had her hair cut the day before yesterday,didn't she?
You had your watch repaired yesterday,hadn't you?
结构一样，照理说第二个应该用didn't you 因为两句中的had都是have得一般过去式，反义疑问句应借助助动词did

unit nouns单位名词 mass noun物质名词

楼主是否明白？？？

Answer 2

一。Don't let the children stay up too late on weekends, will you?(说话的人不包括在内，你们不会……，是吗？）
Don't let the children eat a lot of sweets,shall we?（说话人包括在内。我们不会……。是吗？）
和let's...,shall we?
let us.../will you 一样的道理
二、
She had her hair cut the day before yesterday,didn't she?（正确)
You had your watch repaired yesterday,hadn't you?(错误，应用didn't you)

Answer 3

1的话你就太勉强了。
你想：第1句话。说话的人没有帮自己的主观意念放进去。用WILL YOU。难道不行吗？而第2句话。是争对大家（包括自己）说的。用SHALL WE 。也就是说。如果是完形，应该结合语境，我们老师经常说。

然后第2小句貌似错了。哪有watch repaired，加HAD ，3个动词一个句？

Answer 4

3.mass noun是物质名词，unit noun是表计量单位的那种词