The grammatically correct way would be: To whom did you sell your old car?
"why don't you?" is a question. "why you don't" is a command. Why you don't? is not a correct question. Also it is not a command. Why can be used to give a suggestion or piece of advice eg. 'Why don't you sell your car by advertising it in the paper?' I think 'why you don't' is a variation on this usage eg 'Why you don't sell that car I'll never know'
Yes. "The car that just passed was theirs" is grammatically correct.
Yes, the sentence "Yesterday Tom washed the car" is grammatically correct.
Yes, very correct.
Only if you are using "make" as a noun that refers to a brand of something, for example, a car. You could ask, "What make is your car?" and get the answer "A Honda".
I think the only one that is grammatically incorrect is "Us students have a lot of work to do" it should be "WE students have a lot of work to do" .....
The sentence "He gets farts in the car" should be written like this. "He gets in the car and farts" or "He farts in the car
Verb
"to sell" would be correct. You sell your car and made a sale.:)
Only if you are car surfing (riding on the top of a car with your hair whipping in the wind as it is speeding down the road). The more commonly used sentence would be "I'm in the car" which means you are sitting in the car.
I did not sell my car, I still have it. You do realize your question makes absolutely no sense?
yes....you can sell one with out the windshield if you wanted.....The question should be would some one buy a car with a chipped windshield!