1. Listen! I **think** someone **is knocking** at the door.
2. We **do not know** why Sarah is upset, but she **has not spoken** to us for ages.
3. The earth **circles** the sun once every 365 days.
4. Why **are you staring** at me? I suppose you **have not seen** a woman on a motorbike before!
5. How many times **have you seen** him since he went to Edinburgh?
6. Trevor and Laura like Scrabble. They **play** it most evenings.
7. The number of vehicles on the road **is increasing**.
8. 'Sorry I'm late.' 'That's all right. I **have not waited** long.'
9. Mrs. Green always **goes** to work by car, but this week she **is traveling** by bus.
10. We **are** from France. We **have been** there for 20 years.
11. These flowers are dying. You **have not watered** them for ages.
12. Mai **has lost** her keys, so she can't get into the house.
13. I'm afraid I **have not finished** typing those letters yet. I **have been dealing** with customers all morning.
14. A: What **does your father do**?
B: He **is** an architect but he **is not working** at the moment.
15. A: **Have you ever seen** a lion?
B: Yes, I **have seen** it since I was a child.