16-20 May: For, Since, Ago etc

For, since and ago are used to talk about time.

FOR	For is used to indicate a period of time. How long are you staying in London? I'm staying for a week. For is often used with the Present Perfect. I have been waiting at the bus stop for 10 minutes. I have lived in this country for 5 years. For can be used with other verb tenses : Present : I go on holidays for two weeks every summer. Past : When I was sixteen, I stayed in London for two months. Future :While I am in the USA , I will be in New York for two days.
SINCE	Since is used to refer to the starting point of actions or situations. It is generally used with the Present Perfect. I have been waiting for the bus since 8 o'clock. I live in Tokyo. I have lived in Tokyo since January 2010. I have been learning English since the beginning of the year.
AGO	Ago is used to say when past events happened, going back from today towards the past. The verb is in the Past Tense. I came to Tokyo two years ago. I arrived at the bus stop 10 minutes ago. The company was founded 30 years ago.

And now some exercises:

http://www.learn-english-today.com/lessons/lesson_contents/exercises/for-since-ago_quiz1.html

http://www.englishwsheets.com/for-since-2.html
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