Complete the sentences with the correct preposition in brackets

1. We will be gone for two days. (for / since)

2. I have known him for three years. (for / since)

3. I will arrive at six o'clock. (at / in)

4. He has been gone since Friday. (for / since)

5. She is leaving in five minutes. (at / in)

6. I have known her since last year. (for / since)

7. We expect them on Wednesday. (in / on) 

8. We waited for fifteen minutes. (for / since)

9. Columbus crossed the Atlantic in 1492. (at / in)

10. She will call us at half an hour. (at / in)