Você sabe usar adequadamente as preposições in, on, at? Elas podem ser usadas para designar tempo ou lugar.
Abaixo seguem algumas dicas para estudo e aprendizado do uso de IN, ON, AT.
PREPOSTION OF PLACE
In
Use ‘in’ with spaces that you can physically walk into, or place something into:
in a room / in a building
in a garden / in a park
Use ‘in’ with bodies of water:
in the water
in the sea
in a river
Use ‘in’ with lines:
in a row / in a line
in a queue
At
Use ‘at’ with places in a town, city or other community:
at the bus-stop
at the door
at the cinema
at the end of the street
Use ‘at’ with places on a page:
at the top of the page
at the bottom of the page
Use ‘at’ in groups of people:
at the back of the class
at the front of the class
On
Use ‘on’ with vertical or horizontal surfaces that you can lay something onto, or attach something to:
on the ceiling / on the wall / on the floor
on the table
Use ‘on’ with small islands:
I stayed on Maui.
Use ‘on’ with directions:
on the left
on the right
straight on
IMPORTANT NOTES
In / at / on the corner
We say ‘in the corner of a room’, but ‘at the corner (or ‘on the corner’) of a street’
In / at / on the front
We say ‘in the front / in the back’ of a car
We say ‘at the front / at the back’ of buildings / groups of people
We say ‘on the front / on the back’ of a piece of paper
PREPOSTION OF TIME
In
Use ‘in’ with months, years and periods of time such as decades or centuries:
in January
in 1978
in the twenties
Use ‘in’ a period of time in the future to express that an action will occur after that amount of time:
in a few weeks
in a couple of days
At
Use ‘at’ with an exact time:
at six o’clock
at 10.30
at two p.m.
On
Use ‘on’ with days of the week:
on Monday
on Fridays
Use ‘on’ with specific calendar days:
on Christmas day
on October 22nd
Se quiser testar seu aprendizado, faça o teste online. A correção é automática e você já fica sabendo quanto tirou. Depois me diz qual foi a sua nota.
http://esl.about.com/library/quiz/blgrquiz_prep1.htm
Paula Lyra ELT School 
