Question

помогите пожалуйста.
write a or an.
1.an old book
2...window
3...horse
4...airport
5...new airport
6...organisation
7...university
8..hour
9...economic problem

Answer 1

2...a window
3...a horse
4...an airport 
5...a new airport
6...an organisation
7...a university
8..an hour
9...an economic problem