Ex3:

1. have

2. not get

3. have

4. can

Ex4

1. have just decided

2. has come

3. has been

4. have you ever been

5. has Lan done

6. have you ever eaten

7. haven't worked

8. have gone

9. hasn't played

10. haven't had

11. haven't gone

12. have been

III.

1. Because Mary was sick, she couldn't go to school.

2. I haven't met him for 3 years.

3. Lan finished her homework, so she went out.

4. He likes doing morning exercise.

5. We started learning English 3 years ago

bai 3

1,have

2,not get

3,have

4,speak

bai 4

1,have decided

2,has come

3,has been

4,have ever been

5,has lan done

6,have you ever eaten

7,have not worked

8,have gone

9,has not played

10,have not had

11,have not gone

12,has been