一、主句谓语动词是现在或将来时，从句谓语动词可以用任何需要的时态。
I wonder what he is doing now.
我想知道他现在在干什么。
Do you know when and where he was born?
你知道他在何时何地出身吗？
I'll write to tell him where I 'll meet him.
我将写信告诉他我将在哪里与他碰面。

二、主句谓语动词是过去时，从句谓语动词一般需用过去时。
（1）从句与主句的谓语动作同时发生，从句用一般过去时或过去进行时。
I thought that he studied hard.
我认为他学习很努力。
He told me his son was watching TV.
他告诉我他的儿子在看电视。
（2）从句谓语动作在主句谓语动作之后，从句用过去将来时。
He said he would spend his holidays in Qingdao.
他告诉我他将在青岛度假。
（3）从句谓语动作在主句谓语动作之前，从句用过去完成时。
They told me they had waited for me half an hour.
他们告诉我他们已经等了我半小时了。
（4）从句如果有表示过去某一具体时间的状语，仍用过去时。
She told me her brother died in 1945.
她告诉我她的哥哥（弟弟）死于1945年。

三、从句时态不受下列客观的条件影响。
（1）从句说明的是不受时间限制的事实或真理（客观真理）。
The teacher told us that the earth turns from west to east.
老师告诉我们地球自西向东转。
He said Asia is the largest continent.
他说亚洲是最大的大陆。
It was true that water freezes at thirty-two degrees Fahrenheit.
水在的确是在32华氏度结冰的。
（2）当从句表示的是反复出现的时态不变。
She told me that she gets up at six o'clock every morning.
她告诉我她每天早晨6点起床。
He asked me when the train usually starts.
他向我询问火车通常何时出发。
（3）当从句的谓语动作仍在继续时，或者表示现在仍在的状态时，时态不变。
He said that the workers in that factory are trying to fulfill the task in time.
他说那家公司的员工正在全力及时完成任务。
She told me the other day that she is only 10.
她告诉我那天她只有10岁。
（4）当从句的动作状态还未发生，要用一般式表示。强调与现在的联系。
He said he will wait for me this evening.
他说他今晚将等待我。