"I never listen to the radio unless I rent a car.

I don't listen to the radio very much, but that could be because I don't have a car.
I don't listen to the radio very much, but that could be because I don't have a car.
I don't listen to the radio very much, but that could be because I don't have a car.
I don't listen to the radio very much, but that could be because I don't have a car.