Choice of modal verb

Hello,
I have to rewrite these sentences using a modal verb:

1. Possibly, She is not Anil's sister.
A. She may not be Anil's sister.
B. She can not be Anil's Sister.

2. Perhaps we will go to Shimla next month.

A. We may go to Shimla next month.
B. We can go to shimla next month.
C. We might go to Shimla next month.

3.My sister was able to read alphabet when she was 18 months old.

A. My sister could read alphabet when she was 18 months old.

4. It is necessary that you do not wash car. (The paint is still wet).

A. You should not wash the car.

5.It is necessary that you do not wash car. (It is clean)

A. You need not to wash the car.

6. I am certain that they have left already.

A. They must have left already.

7.Do you allow me to use you phone?

A. May I use your phone?

Are these correct?

Thanks.