4. 完成进行时

　　完成进行时是完成时的强调形式，有现在完成进行时，过去完成进行时，将来完成进行时。

　　（1）现在完成进行时表示过去某一时刻之前开始的动作或状态一直延续到过去某一时刻。例如：

　　I have been looking for my lost book for three days， but I still haven't found it.

　　（2）过去完成进行时表示过去某一时刻之前开始的动作或状态一直延续到过去某一时刻。例如：

　　It had been raining cats and dogs for over a week and the downpour had caused landslides in many places.

　　（3）将来完成进行时表示在将来某一时刻之前开始的一个动作或状态一直延续到将来某一时刻。例如：

　　By the time you arrive tonight， she will have been typing for hours.

　　四：时态一致

　　时态一致是英语四、六级考试的一个重要内容。通常应由主句谓语的时态决定从句的谓语时态。一般原则是：

　　1、当主句谓语使用现在时或将来时，从句的谓语根据具体情况使用任何时态

　　He says that he lives in Wuhan.

　　We hope that there will be many people at your party today.

　　“Did you hear that Bill finally sold the house？” “Yes， but I don't know who bought it.”

　　“There's a lot of excitement on the street.”

　　“There certainly is. Do you suppose the astronauts have returned？”

　　2、当主句谓语使用过去时的时候，从句的谓语必须使用过去范围的时态

　　He said he was writing a novel.

　　The teacher wanted to know when we would finish the experiment.

　　He said his father had been an engineer.

　　3、当从句是表示没有时间概念的真理时，从句的谓语应使用一般现在时。例如：

　　The teacher told them since light travels faster than sound， lightning appears to go before thunder.

　　注：在此种情况下，即使主句谓语用了过去式的各种时态，从句谓语也应用一般现在时。

　　4、从句谓语只能用虚拟语气的情况

　　利用时态一致原则确定从句动词时态时，还应注意，若主语动词是表示命令、请求、要求、建议、劝告等的动词，从句谓语只能用虚拟语气，不能遵循时态一致原则。例如：

　　We insisted that we do it ourselves.