Unit 2 What is happiness to you?
a. sat b. had sat c. had been sitting d. was sitting answers: cacd4. 一般过去时和过去进行时的区别 1). 一般过去时表示在过去某时发生的动作或存在的状态（包括过去习惯动作），常与just now, a moment ago, yesterday, last week(month, year), the day before yesterday及表示过去的时间状语从句。如
i was sixteen years old last year. he worked in a factory in 1986. i met her in the street the day before yesterday. he often swam in the river when he was young.2). 过去进行时表示过去某一段时间或某一时刻正在进行的动作。常与之连用的时间状语有，at that time/moment, (at) this time yesterday (last night/ sunday/week…), at+点钟+yesterday (last night / sunday…)，when sb. did sth等时间状语从句。
eg. what were you doing at seven p.m. yesterday?
i first met mary three years ago. she was working at a radio shop at the time.
i was cooking when she knocked at the door.3). 一般过去时往往表示某一动作已经完成，而过去 进行时却表示动作在持续或未完成。
i saw you while you were speaking to joan.注意：有的过去时间状语既可用于一般过去时，也可用于过去进行时，但含义不同。如： she wrote a letter to her friend last night.
她昨晚给她的朋友写了封信。(信写完了)
she was writing a letter to her friend last night.
她昨晚一直在给她的朋友写信.（信不一定写完）4). 过去进行时的时间状语从句
(1). when 和while引导的状语从句
while表示一段时间，因此它所引导的状语从句中，谓语动词常用进行时态，如：
when/while we were having supper, the light went out.(2). when用作并列连词时，表示主句动作发生的过程中，另一个意想不到的动作发生了。
i was walking in the street when someone called me.
我正在街上走时突然有人喊我5.过去完成时1)在某一过去时间以前或过去某事之前已发生并完成的动作。by the end of last month they had treated 3,000 patients.by the time she competed in the new york goodwill games, she had been a dedicated junior gymnast for eleven years.2)表示一种未实现的愿望和想法。i had hoped to go on monday, but i couldn’t get away.i had thought that he was our english teacher.3)用与hardly…when, scarcely…when, no sooner…than句型中。hardly had he finished his homework when we went home.6. 过去完成时与一般过去时1). 历史事实通常用一般过去时表示，如：
they learned that lincoln led the american war.
he told the students that hitler killed millions of jews.
