AGO - used to indicate a point in time in the past. The verb is in the past tense.
a) The company was founded more than 35 years AGO. b) I got to the office half an hour AGO. c) The cow was domesticated about 8000 years ago.
FOR - used to indicate a period of time. Verbs describe actions taking place during the period. Many tenses can be used.Emphasis is on the length of the period.
a) The company has been in business FOR more than 35 years. b) I have been at work FOR half an hour. c) The cow has been domesticate FOR about 8000 years.
SINCE - used to indicate a period of time. The verb is generally in a perfect tense. Emphasis is on when the action described by the verb began.
a) The company has been in business SINCE 1970. b) I have been in the office SINCE nine o'clock. c) The cow has been domesticated SINCE about 6000 B.C..
I saw Bill a few days _____. He told me he's planning to retire next month.
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This bill has remained unpaid _____ six months, in spite of reminders.
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Have you had the same job _____ you started to work for the company?
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Crawford got his start in the electronics field about twenty years _____.
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The electricity has been off _____ early this morning. We can't get any work done.
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When Jim took charge of the company six years _____, he was just 30 years old.
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The transistor was invented about 60 years _____. Electronics has changed a lot since then.
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That gentleman has been waiting to see you _____ over an hour. May I send him in?
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When are you going to pay that bill you received six months _____.
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I've been waiting for Ted to ask for a raise _____ the last three months.
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It's been six months _____ we sent you that bill and you still haven't paid!
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We've been friends _____ a long time. You can tell me if something is wrong.
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How long _____ did Jensen join the firm?
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The new equipment arrived an hour _____. The men are setting it up now.
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Bill's been taking it easy _____ he had his heart attack.
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Jim! I don't think I've seen you _____ you retired last year. How've you been?
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We've been looking for a replacement _____ Jensen announced his retirement, but so far we haven't found anyone.
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How long is it _____ we've had an order from ESI? Maybe you should give them a call.
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Bill's been ill _____ several months. He's not expected to return to work.
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How've you been _____ we last met, when was it, a couple of years ago?
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He's been running the company _____ ages now.
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Crawford's been in this field _____ over twenty years. I think we can trust his judgment.
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Profits started dropping off about a year _____ due to increased competition.
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I used to run five miles a day, but I haven't felt up to it _____ a month or so.