C. 从句动作发生在主句动作之前，从句须用过去完成时。例如：
He said he had posted the letter。 他说已经把信发了。
They asked me whether I had been there before. 他们问我以前去没去过那里。
但是，如果从句有具体的过去时间状语，尽管从句动作发生在主句动作之前，有时仍用一般过去时。例如：
She told me her brother died in 1960. 她告诉我她哥哥1960年去世的。
They said they checked everything yesterday. 他们说昨天他们全部检查过了。
另外，从句说的是一般真理或客观事实，即使主句用过去时态，从句仍用一般现在时。例如：
The teacher told the pupils that the earth is round. 老师告诉学生们地球是圆的。
Somebody told me you are a writer. 有人告诉我你是个作家。
除了宾语从句外，其他名词性从句(主语从句、表语从句和同位语从句)一般也要遵守这种时态呼应的规律。而状语从句和定语从句则是根据本身意思的需要选用适当的时态。例如：
He saw the boy whose mother is our teacher. 他见过那个他妈妈是我们老师的男孩。
It was not so hot yesterday as it is today. 昨天没有今天这样热。