XI. 

1. At, on 

2. Of

3. At

4. For

5. To 

6. On

7. For

XII.

1. You should not allow a three -year -old child to walk home alone.

2. Martin’s poor health doesn’t prevent him from enjoying life.

3. I haven’t seen Bob since I was in HCM city.

4, The manager threatened Brian not to select him for the team if he didn’t train harder.

5. Apart from the students, she was absent  from class.

XII.

1. The teacher told students to take three examminations for the following week.

2. Television plays such an important role for people in life, so it is essential for us to decide whether it is bad. 

3. Because of the terrible weather in winter, so it is better for his physical exercise students in doors rather than outdoors.

4. We are close friends because we have many things in common.

5. About five million bottles of champagne is producted in France every year.