When the object clause is used as the direct object, can it be omitted, for example, she tells us what to do.

This leads to the situation that the object clause cannot be omitted.

(1) When connecting two or more object clauses, the first one can be omitted or omitted, but the others cannot be omitted to avoid misunderstanding:

Galileo's observation shows that Copernicus, another great astronomer, was right. The earth goes around the sun, not the sun.

(2) that cannot be omitted after prepositions such as except and but.

He is a good student, but a little careless.

(3) that cannot be omitted when it is emphasized at the beginning of a sentence.

I can hardly believe that he said such a thing.

(4) When there is an insertion between object clauses, it cannot be omitted.

I believe everyone can see that Tom is really scared.

(5) When used as a formal object, that is guided by that in the object clause and cannot be omitted.

We thought it strange that Xiao Wang didn't come yesterday.

(6) When answering briefly in the dialogue, if the object clause led by that appears independently, it cannot be omitted.

-What did he say?

He won the first prize in the competition.

(7) The object clause led by that can be followed by a double-object verb. When used as a direct object, that cannot be omitted.

This foreign friend told us that Chinese is one of the most difficult languages to learn.

(8) When the adverbial is immediately before or after the object clause led by that, that cannot be omitted.

He suddenly saw the boy and immediately realized that he had seen him before.

(9) In direct speech, when the object clause led by that is separated from the main sentence, that cannot be omitted.

"I'm sorry to say," he said, "that you are not the right person for this job."