<例句>
They were at dinner when I called.
我打电话时他们正在吃饭。
<语法分析>
be+某些介词短语，在时态上相当于进行时，这些介词短语有be at sth.,be in sth.,be under sth.,be on sth.和be after sth.等。在与表示感情的形容词连用时，at可以代替“听”、“看”等动词。在与go,come和return等动词连用时，for可以代替后面表示“目的”的动词。for在与start,leave和set等词连用时，相当于汉语的“走”、“到”、“往”等意思。还有些介词短语可代替动词不定式短语，作定语。
<触类旁通>
(1)What are you at now?
你在干什么?
语法分析：be at sth.表示在干什么事情。
(2)Matter is always in motion.
事物时时刻刻在运动。
语法分析：be in sth.表示进行的事情。
(3)Chickens are on sale.
小鸡在出售。
语法分析：be+某些介词短语，在时态上相当于进行时。
(4)He was greatly surprised at the bad news.
他听到这个坏消息大吃一惊。
语法分析：在表示感情的形容词连用时，at可以代替“听”、“看”等动词。
(5)She is also invited to the hall.
她也被邀请参加这个舞会。
语法分析：to在与go,come,invite等动词连用时，可以代替“出席”、“参加”等动词。
(6)She has left Japan for America.
她已离开日本去往美国了。
语法分析：for在与start,leave和set等词连用时，相当于汉语的“走”、“到”“往”等意思。
<巩固练习>
(1)The students were very glad _____ the film.
(2)She has gone _____ a meeting.
(3)He came _____ his wallet.
(4)I am going out _____ dinner.
(5)She set traps _____ mice.
(6)I'll start _____ England at six early tomorrow morning.
(7)I am _____ the plan.
(8)My brother is _____ school.
(9)It's time _____ breakefast.
(10)She often writes _____ my pen.
(11)I go to work _____ bike.
<参考答案>
(1)at (2)to (3)for (4)for (5)for (6)for (7)for (8)at (9)for (10)with (11)by
