1. does he work now?

3. the classes start early in the morning? - yes.

5. David finally sold his old computer

7. Alice didnt come to the conference

9. i worked all day long in the laboratory on Friday

11. when she entered the classroom, the teacher was explaining the new topic

13 it was already snowing badly for about two hours when they went out of school.

15 i have been told that its been around a month as you are reading this book. Its time to return it to the library

17 we ae going to buy new reagents

19 they are going to complete their experiments tonight