Question

英语高手：定语从句问题请教：It's the third time __________you made the same mistake.

请说明理由，究竟是不是定语从句？

Answer 1

定语从句有限制性和非限制性两种。限制性定语从句是先行词不可缺少的部分，去掉它主句意思往往不明确；非限制性定语从句是先行词的附加说明，去掉了也不会影响主句的意思，它与主句之间通常用逗号分开，例如：
This is the house which we bought last month. 这是我们上个月买的那幢房子。（限制性）
The house, which we bought last month, is very nice.这幢房子很漂亮，是我们上个月买的。（非限制性）
2) 当先行词是专有名词或物主代词和指示代词所修饰时，其后的定语从句通常是非限制性的，例如：
Charles Smith, who was my former teacher, retired last year. 查理·史密斯去年退休了，他曾经是我的老师。
My house, which I bought last year, has got a lovely garden. 我去年买的的那幢房子带着个漂亮的花园。
This novel, which I have read three times, is very touching. 这本小说很动人，我已经读了三遍。

3) 非限制性定语从句还能将整个主句作为先行词, 对其进行修饰, 这时从句谓语动词要用第三人称单数，例如：
He seems not to have grasped what I meant, which greatly upsets me. 他似乎没抓住我的意思，这使我心烦。
Liquid water changes to vapor, which is called evaporation. 液态水变为蒸汽，这就叫做蒸发。

说明：关系代词that和关系副词why不能引导非限制性定语从句。

Answer 2

that
注：定语从句中只用that 的情况
1 先行词为不定代词: one much everything all any ...
2 先行词被形容词最高级所修饰
3 先行词被序数词所修饰
4 先行词由only ,just ,very, right等修饰
5 在以which 开头的特殊疑问举重，避免重复用that.
6 先行词在从句中担任表语，从句的关系词用that.

Answer 3

固定搭配``
属虚拟语气
It is about /third /high time + that + 动词过去式
同时也是定语从句``

Answer 4

that 在这里不表示任何意思 只起个衔接作用

Answer 5

that