Using a modal auxiliary:

Question

Using a modal auxiliary:
I’m sure the teacher didn’t know that the slow students regarded themselves as inferior in their class.
为什么要加个have？

Answer 1

using a modal auxiliary 意思是让你用情态动词改写句子。本句的意思是"我断定该教师当时不一定知道..."，属于对过去事实的否定推断，按照英语语法，所以应该用情态动词 couldn't 加 have known。

Answer 2

改写：

I'm sure the teacher can't have known that the slow students regarded themselves as inferior in their class.

 can't have known不可能已经知道，对已经发生的动作的情态。

He can't have left.他不可能已经走了。

Answer 3

英语表达中，对过去状态进行推测时，肯定性推测用must have done/ been…，否定性推测用wouldn't/couldn't have done/ been….

原句可改写成

The teacher couldn't have known that the slow students regarded themselves as inferior in their class.

Answer 4

Using a modal auxiliary:
I’m sure the teacher didn’t know that the slow students regarded themselves as inferior in their class.
为什么要加个have
原句可改写成
The teacher couldn't have known that the slow students regarded themselves as inferior in their class.

Answer 5

没看到have？