宾语从句的时态呼应

如果主句为过去时态，那么宾语从句通常要采用相应的过去时态。

I didn't know when he leaved the office. 我不知道他什么时候离开办公室。
I was so glad that they were doing well. 我很高兴他们做得很好。
He didn't think that Peter had told the true. 我不认为彼得讲了实话。
She hoped she would go back home immediately. 她希望立即回家。
He asked her if she was going to set off early next morning. 他问她是否第二天一早就出发。

注意， 在一些特殊情况下， 从句时态不随着主句的时态变化。

1) 表示永恒真理时。
Scientists proved that light travels faster than sound. 科学家证明了光速比声速快。
When we were children, we were told that China is the east of the world. 我们是小孩子的时候， 人们就告诉我们说中国在世界的东方。

2）在口语中为了避免误会时也可以不变。
She said she's leaving tonight. 他说她今晚走。
Tom said he'll do it. 汤姆说这事他来做。
He told me just now that his wife is ill. 他刚才告诉我他妻子病了。

3) 使用虚拟语气时。【高中以上】
She demanded that I pay her immediately. 他要求我立即付款给她。
He insisted that Jennie send her to dancing school. 他坚持要珍妮送她进舞稻学校。
They proposed that Mr. Smith be the chairman. 他们提议史密斯生生担任主席。