时态一致
1)并列谓语的时态一致。
【例如】Yesterday I went shopping, bought some books and had dinner at a good restaurant.
The soldier looked at him, exchanged glances with his comrade and took out the gun.
2)主从复合句的时态一致。
a)主句为现在时、将来时、现在完成时，宾语从句谓语动词时态按情况而定。
【例如】
I wonder what will happen tomorrow.
I wonder what happened to him yesterday.
I wonder what is happening now outside.
b)主句为过去时态，宾语从句一般用过去时态。如果宾语从句说明的是客观真理，用一般现在时。
【例如】
He told me he made a big mistake.
He told me he would go to Beijing the next day.
He told he had finished his task.
The teacher told students that the earth moves around the sun.
3)定语从句和比较状语从句时态不受主句影响。
【例如】
The universityswhereshe is studying was founded in 1950.
You now speak English better than you spoke it last year.
4)时间和条件状语从句中，常用现在时表示将来。
【例如】
We will cancel our trip if it rains tomorrow.
I will go to visit the Summer Palace as soon as I arrive in Beijing.