一、动词的时态
1．一般现在时
(1)表示经常性、习惯性的动作和现在的状态、特征。句中常用often, usually, every day等时间状语。
Works of popular writers often have a lot of readers.
On Monday mornings it usually takes me an hour to drive to work although the actual distance is only 20 miles.
(2)表示客观事实、普遍真理或自然现象，无论在什么情况下都用一般现在时表示。
“Life is like walking in the snow，” Granny used to say，“because every step shows.”
—So what is the procedure?
—All the applicants are interviewed before a final decision is made by the authority.
(3)在时间状语从句和条件状语从句中，用现在时代替将来时。
My parents have promised to come to see me before I leave for Africa.
(4)表示按计划、时刻表规定要发生的动作，但限于少数动词。如begin, come, leave, go, arrive, start, stop, return, open, close等。
The flight takes off at 2：30 every Wednesday and Friday.
2．一般过去时
(1)表示过去的事情、动作或状态，常与表示过去的时间状语连用(或上下文语境有暗示)；用于表示过去的习惯；表示说话人原来没有料到、想到的事。
I didn’t realize then, but becoming a pilot makes me a better surgeon.
Michael’s father always helped the poor as he believed it made everyone happier.
I was lucky: I became a pilot in 1970, almost ten years before I graduated from medical school.
(2)注意句型：was/were about to do ... when ...中when后从句的动词用过去式。
I was about to go to bed when the telephone rang.
