第1个回答 2023-07-30
1. 一般规则
1) 若主句谓语动词是现在时态或将来时态，从句中可根据意思需要，选用任何时态。例如：
I know that he is (was, will be) in Beijing. 我知道他（曾、将)在北京。
We shall find out when they arrived (will arrive). 我们将查明他们是何时（或将于何时）抵达的。
2) 若主句谓语动词是过去时态，从句中一般要用过去时态。
(1) 如果从句动作与主句动作同时发生，从句用一般过去时或过去进行时。例如：
They could not understand why he spent so much mcxiey on clothes. 他们不明白他为什么花那么多钱买衣服。
The professor said that the students were having an exam. 那位教授说学生们正在考试。
(2) 当从句动作发生在主句动作之前，从句要用过去完成时。
例如：
She told me that she had been offered a very well-paid position. 她告诉我有人给她提供一个高薪的职位。
I had to work late last Sunday because I had been asked to write an article for a magazine. 我昨晚不得不工作得很晚，因为有人请我为一家杂志写稿。
We found the train had left. 我们发现车开了。
(3) 当从句动作发生在主句动作之后，从句中要用过去将来时。例如：
Smith hoped that the boss would give him an early reply. 史密斯希望上司会尽早地给他一个答复。
The doctor said that she was going to have twins. 医生说她将生一对双胞胎。
【注】有些形容词后面也可跟一个从句，这种从句通常也被看作宾语从句，其谓语也应与主句谓语的时态保持一致。例如：
I’m confident that I’ll pass the exam.我有信心通过考试。
She was afraid that the dog would bite. 她担心那条狗会咬人。
He was not sure whether his application had been accepted. 他不敢肯定他的申请是否已被接受。
2. 特殊规则
1) 当从句表示客观事实或真理时，其时态可不受主句谓语的影响，而用一般现在时。例如：
Kepler proved that the sun is the centre of the solar system. 凯普勒证明了太阳是太阳系的中心。
The teacher told the children that water boils at 100 ℃. 老师告诉孩子们水在摄氏一百度沸腾。
2) 时态呼应多见于宾语从句、主语从句、表语从句和同位语从句，状语从句和定语从句中可根据意义的需要来选用任何时态。例如：
I didn’t go to the ball because I am not fond of dancing. 我没有去参加那个舞会因为我不喜欢跳舞。
He spoke much more fluently at the meeting than he usually does. 他在那次会上的发言比他平时说得流利得多。
The car which often breaks down was bought 10 years ago. 那辆经常出毛病的车是十年前买的。