①表示时间、地点、价钱、速度、年龄

②表示动作之方向、目的：朝，向

③固定词组中

① at ten o'clock, at the school, at the age of 40, at a lower price,

at (a speed of ) 150 kilometres an hour

②He threw a stone at a dog.

③ at first, at last, at (the )most,

at (the )least, at once, at present,

at home, at night, at the beginning,

at the same time, not at all etc. ①表示时间：在......世纪，......年......月

②在......范围和空间内

③穿着某种衣服

④固定词组

①in the 20th century，in May, in the 1870s

② in a village, in a tree, in bed,

in the sun, in the rain, in her hand

③ in white /blue /yellow /green /red.

④ in all，in public，in turn，in one's opinion，in secret，in a way，in fact,

in front of，in (the)future，in time，

in trouble，in a word， in other words，

in a hurry，in the world ①表示接触面

②在某天、某天的早晨、上午、晚上

③关于，论及

④（表示时间）在......时候；刚一......就

⑤固定结构

①There is a picture on the wall.

②on Saturday/Wednesday，on Oct 10th, 2003，on the morning /evening of Oct 10th

③ a discussion on whether students can chat on line, a book on basic English

④On hearing the news, they jumped with joy.

⑤on duty，on time，on fire，on the one hand，on the other hand，on sale，on purpose，on the left /right，