For example, a car can not run anymore because one of the tires is flat. However, everything else on the car still works, so you don't want to dump the whole car only because one of the tires is flat. D is saying that if you can change the old tire into a new one that won't get flat easily, that would be nice.
For example, a car can not run anymore because one of the tires is flat. However, everything else on the car still works, so you don't want to dump the whole car only because one of the tires is flat. D is saying that if you can change the old tire into a new one that won't get flat easily, that would be nice.