The correct sentence is A) My car is old and gets bad gas mileage. Having bad gas mileage is an ongoing thing that will never change unless you get a different car, so none of the other choices make sense.
Out of the sentences provided in the options, only option (A) is correct.
The gas mileage will always remain the same, no matter how new or old the car is unless one is to buy a new car replacing it. No car will have a differing gas mileage within one single car, making option (B) invalid. Option (C) is wrong in the use of "were" and option (D) is also wrong in it's use of "be".
