Plural And Singular Nouns

1) The cat is sitting on my bed.(bed)
2) There are five pencils on my desk. (pencil)
3) I have two sisters. (sister)
4) They are riding their bikes.(bike)
5) We have a dog.(Dog)
6) How many books do you have in your bag? (book)
7) My mother has a new computer. (computer)
8) There are three windows in the room. (Window)
9) Susan has four posters. (poster)
10) There is one pen on the floor. (pen)