Sure! Here are the completed sentences:

1. The girl is **a** pilot.
2. I've got **an** idea.
3. My wife is **a** doctor.
4. They've got **an** excellent solution.
5. She has **a** strong alibi.
6. I saw **a** movie last night.
7. Sara can play **the** guitar.
8. I bought **a** pair of shoes.
9. Leipzig has **an** airport.
10. My brother is **an** artist.
11. This is **an** easy question.
12. This is **an** expensive bike.
13. She's reading **an** old comic.
14. Look! There's **a** bird flying.
15. They are staying at **a** hotel.
16. Who invented **the** telescope?
17. I would like **a** piece of cake.
18. It's **a** short walk from there.
19. Is there **a** shop in the hospital?
20. Suzanne works at **the** hospital.