表进行意义的四类介词短语
一、at+名词
He was at dinner when I came. 我来时他正在吃饭。She stayed at work when everybody else had gone home. 别人都回家了,她却还在工作。The country has been at war with its neighbour for three years. 这个国家与邻国交战已有三年了。类似的还有:at cards 在玩牌            at work 在办公 at play  在玩耍     在吃中饭    at rest在休息        at table在吃饭at school在上学       at church在做礼拜at peace和平时期at press正在排印有些结构可能带有冠词或物主代词:at one’smeals在吃饭&nb 10.5pt; mso-ascii-font-family: 'TimesNewsp;at one’s study在学习at thepiano在弹钢琴at the end (of)在结束时at the desk在读书

二、in+名词
He is inthe army.他正在当兵。He’s beenin politics all his life.他一生从政。Her husbandwas in business.她丈夫是经商的。He lookstired. He is in need of a rest.他看来很累了,需要休息一会儿。类似的还有:in action在运转in progress在进行inoperation在运行中有些结构可能带有冠词:in thecourse of在……过程中in the act of正在做……时

三、on+名词
Are youhere on business or for plea
你是来办事还是来玩?The typist is away onholiday this week.打字员本周休假。The man onwatch didn’t notice the danger.值班的人没有注意到这危险。We have soarranged matters that one of us is always on duty.我们做了这种安排,以便我们总有一个人值勤。类似的还有:on guard在值勤on leave在休假on holiday在度假on strike在罢工on sale出售on loan借贷有些结构带有冠词:on the boil水正在开on the move 在移动,搬迁,离开on themarch在行军on the watch注意,提防on the flow在涨潮on the turn在转折中on theincrease正在增加on the go正在活动,正在奔走on the air正在广播on the fly正在飞行

四、under+名词(名词前有时有冠词修饰)
Don’tworry. Everything is under control.别担心,一切都在控制之中。That has norelation to the matter under discussion.这和讨论的问题没有关系。类似的还有:underdevelopment在发展中 under observation在观察中undertest在被测试 under construction在建设中under fire在炮火中        under examination在检查(调查)中underconsideration在考虑中under repair;在修理中