1.an
2.an
3.a
4.zero
5.an
6.a
7.a
8.a
1.Intelligent relatives have read all the books i have.
2.cunning students have introduced themselves as another boys.
3.Generous people ordera lot of dishes in the cafe.
4.cold cellars were closed for summer
5.тут никак нельзя. Ну как бы в задании указано что сделать во множ.числе там где возможно