一般现在时：every day, every year, always, usually, often , sometimes , hardly ,never等.
一般过去时:ago, yesterday, last year, last week, just now (刚才), the day before yesterday(前天）, in 1999 , in the past (在过去）
一般将来时：tomorrow, next year , next week ,the day after tomorrow (后天）, in the future
现在进行时：now, Look !Listen !It's 7 o'clock , we are doing . (现在几点了我们正在...）
过去进行时：at this time of yesterday (在昨天的这个时候）at that time , at 7 o'clock last night现在完成时：already, ever, never, yet, so far(到目前为止）, in the past/ last few years
(在过去的几年间）,over the years （近年来）
过去完成时：1. by the end of last year.
e.g. By the end of last term, we had learned 5000 new words.
2.By the time sb. +动词过去式
e.g. The bus had already left by the time I got there.
3. 宾语从句
过去完成时的动作发生在过去的过去. He said he had been to Beijing twice.
他说他已经去过北京两次.
（因为“说”said就是过去式,而去北京的动作发生在说said 的过去,
所以用过完而不用现完.）