Put the sentences into Plural

Example : a child is a boy or girl

Children are boys or girls

1 . A dog is an animal

2. A potato is vegetable

3. he is a student

4. I am doing my homework

5. he was studying when I came

6. she herself writes the letter

7. A business consist of an operation

8. she performs a service by answering a question

9. what is the difference between you & me ?

10. his friend is also my friend

11. the student has almost finished doing it

12. has she ever been studying abroad?
13. The earthquake cause a great disaster

14. does he understand the lesson ?

15. there is a boy & girl in the class