下面说说这三个介词在表示地点时用法的区别,口诀如下：
on,in,at表地点,on“在之上”接触面,
“靠近、接壤、左右边”①； in“在里面”和“中间”②；
at表示小地点,“入口、车站、影剧院”③；
home出现定语、冠,须用in把at换④；
“夜间、车辆”若有限,及“在途中”on在前⑤.
说明：
①在表示地点时,指“在……之上（与表面接触）”.例：
There is an English－English dictionary and two grammar books onthe big desk．那张大写字台上有一本英语词典和两本语法书.
“靠近、接壤”及“在左右边”都用on.例：
Korea lies on the northeast of China．朝鲜位于中国东北方.
Tom was sitting on my left when we saw the film yesterday．我们昨天看电影时,汤姆坐在我左边.
②表示“在……里面”（即物体内部）.例：
Jim turned the key in the lock and opened the door．吉姆把钥匙插在锁孔里,转动一下,打开了门.
“在……中间”（即middle前）都用in.例：
Soon they were in the middle of the river．很快他们就游到了河中间.
③at表示一个较小的地点,如在“入口”（entrance）“车站”（busstop,railway station）和“影剧院”（cinema,theater）等名词前.例：
As she walked along,she noticed an old pine tree ahead at the en－trance to a valley．她往前走时,注意到前边峡谷口有棵老松树.
④home前一般用at,但若有物主代词和冠词等定语修饰时,须用in.例：
In Princeton he lived quietly,working at the institute and enjoyinghimself by playing his violin in his simple home．他在普林斯顿过着安静的生活,在研究所工作,在他那简朴的家里拉琴消遣.
⑤“夜间”（night）、“车辆”（bus,bike,train ect．）等名词若有限定词及“在……途中”,介词则用on.例：
1）He was in on that night．他那天夜里在家.
2）My son often goes to school on his bike．我儿子常骑自行车去上学.
3)On the way home my father told me of an incident that tookplace on his first day at school in Mr Crossett’s class．在回家途中,父亲给我讲了他第一天上克罗塞特先生课时发生的一件事.1、Lucy can write a letter___Japanese though she has learned it only a few months.
A.from B.to C.in D.with
2、They will have an English test___two days.
A.for B.at C.in D.after
3、Wu Dong was born___the evening of April 2,1975.
A.at B.in C.on D.to
答案：ccc