1- a
2- an
3-the
4- an
5-an
6-a

1.Their car does 150 miles___an__hour.
2.Where's___an__USB drive I lend you last week ?
3.Do you still live in___the__Bristol ?
4.Is your mother working in__an___old office building ?
5.Carol's father work as__an___electricyan 
6.The tomatoes are 9$___a__kilo
8.What do you usually have for__the ___breakfast ?
9.After this tour you have___the__whole afternoon free to exflore the city

1) an
2)an
3)x
4)an 
5)an
6)a
7)x
8)the