动词时态
动词形态可以简单地分为简单式和完成式两种，就能充分掌握所有的时态变化。时间观念有现在式、过去式、和未来式。把be动词抽离出来当做动词看待，其后的分词则视为形容词补语，不放在动词短语里面，如此，整个时态问题就会简单化。
①简单式
简单式的动词可以清楚交代此动作是发生于哪个时段。
一、过去时间
The movable print was introduced to England in 1485.
I was watching TV when I heard the doorbell.
The witness was being questioned in courd when he had a heart attack.
二、现在时间
如果副词是now ，或者真理及事实要用现在简单式
Buch is the U.S. president.
All mothers love their children.
三、未来时间
There will be a major election in March.
The building will be razed next month.
②完成式
从功能上看，简单式是交代动作发生的时段，而完成式并不对动作发生的时段作明确交代，只表示“曾经”“做过”的意思。
一、现在时间（即到现在为止）
I'm sure I have seen this face somewhere.
二、过去时间（即到过去的某个时间为止）
Many soldierd had died from pneumonia before the discovery of penicilin.
I had been smoking three packs of cigarettes a day before I decided to quit.
在盘林西林发生前，许多士兵死于肺炎。
三、未来时间（到将来的某个时间为止）
Next April,I will have worked here for 20years.
