你问的是宾语从句的语法吗？在直接引语改为间接引语（即宾语从句）时，主句如果是过去时，从句一般要改成相应的过去时态。相应法如下：
一般现在时——一般过去时：She said, "I am fifteen."
She said that she was fifteen.
现在进行时——过去进行时：He told us, "They are watching TV."
He told us that they were watching TV.
现在完成时——过去完成时：Mr. Li said, "I have been to Canada."
Mr. Li said that he had been to Canada.
4. 一般将来时——过去将来时：She said, "We will visit our grandparents."
She said that they would visit their grandparents.
5. 一般过去时——过去完成时：The boy said, "I saw the strange man."
The boy said that he had seen the strange man.
过去进行时不改，过去将来时不改，过去完成时不改。
如果从句为客观真理，用一般现在时，不改。