Articles: a/an, zero exercises

Fill in all the gaps with a/an or write x if there is no article. Use the "Hint" button to get a free letter if an answer is giving you trouble. Note that you will lose points if you ask for hints!
1. I'm having few friends in to coffee tomorrow evening.
2. I'm going to concert tomorrow.
3. I think I've got cold. I think you're getting flu.
4. He wants to make complaint about article in the paper.
5. I had nightmare last night. I saw horse chasing me.
6. I don’t eat meat. I’m vegetarian.
7. He was in very bad temper.
8. If you go by train you can have quite comfortable journey,
9. He broke arm in skiing accident. It's still in plaster.
10. I want assistant with knowledge of English.
11. My house is built of wood.
12. Are you insured against fire?
13. It's time you had holiday.
14. I haven't had day off for month.
15. But I'm not going for holiday; I'm going on business.
16. I wouldn't climb mountain.
17. I have horror of heights.
18. I have headache and sore throat.
19. The prisoner camped in wood but he didn't light fire.
20. I'll pay you hundred week.