Exercise 1: Complete the sentences with SINCE or FOR.  
1. There has been snow on the ground  ______New Year's Day.  
2. The weather has been cold______  a long time.  
3. Maria has studied English ______ less than a year.  
4. Mr. and Mrs. Roberts have been together______  they were in college.  
5. They have known each other  more than fifty years.  
6. We haven't seen Aziz ______  last month.  
7. I've had a cold______  over a week.  
8. I haven't heard from my sister______ the beginning of March.