that引导的宾从不用is,是因为that引导的宾从是一个名词性从句,而名词性从句通常不使用is来连接。is是一个系动词,主要用于连接主语和表语,表示主语的身份、性质、状态等。而宾从通常表示动作或状态的对象,因此不需要使用is来连接。
例如,句子“I know that you are a good student.”中,that引导的宾从“that you are a good student”表示的是动作“know”的对象,因此不需要使用is来连接。
如果要使用is来连接that引导的宾从,则需要将宾从改为一个形容词性从句。例如,句子“I know that you are a good student.”可以改为“I know that you are good.”,其中“good”是形容词,因此可以使用is来连接。
以下是一些that引导的宾从的例子:
I know that you are a good student.
I saw that he was happy.
I heard that the news was true.
I think that this is a good idea.
I want to know that you are coming.
在这些例子中,that引导的宾从都是名词性从句,因此不需要使用is来连接。