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- ?Lv 71 decade agoFavorite Answer
"That" cannot be omitted if it is used as a subject in a clause.
I knew the driver of the car that was crashed in the accident.
"that" here is the subject and is referring to the car and cannot be omitted.
"That" can be omitted if it is used in a noun clause that is the object of a sentence.
He said (that) he would come home late. (that can be omitted)
Everyone thinks (that) it is a very difficult job. (that can be omitted)
When the noun clause is used as the subject of a sentence, "that" is preferred.
Everyone knows (that) he is smart boy. (that can be omitted).
That he is a smart boy is known to everybody. (better to have that)
The last sentence can be written as
The fact (that) he is a smart boy is known to everybody. (that can be omitted)
Here "that" can be omitted because it is a noun clause to tell what the fact is.
2007-11-12 08:56:39 補充：
When that is used as an object, it can be omitted.This is the book (that) everyone likes to read. (that can be omitted)
- ?Lv 61 decade ago
"that" usually can not be omitted. e.g. I believe that no one marries for money, but I know
that money issues frequently lead to marital difficulties.