宾语从句的时态
(1) 若主句是一般现在时、一般将来时或祈使句时，宾语从句根据句子的意义使用需要的时态。如：
We dont know who has broken the window. But we will find out who has done that.
Please tell me where we will go.
(2) 若主句是一般过去时，宾语从句要用相应的某种过去时态，如一般过去时、过去进行时、过去将来时或过去完成时。如：
He said: Im a student. ----- He said that he was a student.
The teacher asked: What is Mike doing? ----- The teacher asked what Mike was doing.
(3) 若宾语从句叙述的是客观真理或永恒不变的规律，则应采用一般现在时，不受主句时态的限制。如： Our teacher said that the earth moves round the sun.