Question

1. Will we use cars 20 years from now?

2. Will we use cars for 20 years from now?
3. Will we use cars for 20 years?
4. Will we use cars since 2002?
5.Will we be using cars 20 years from now?
6. Will we have used cars for 20 years from now?
7. Will we have used cars for 20 years?
8. Will we have used cars since 2002?

(Which ones are grammatical?)

Answer 1

Incorrect:

#2
#4
#6

The others are grammatically OK.