Bio diesel is a fuel that can be used in most road vehicles instead of gasoline. Its use produces significantly less air pollution, Market research predicts that as this fuel becomes more widely available over the next ten years or so , hundreds of thousands of drivers will use it . We can only conclude , then, that many people care about reducing pollution.

I feel like taking a stab at this...

Let's assume the answer is choice 'A'. For these individuals, we can - at least, qualitatively - measure their interest in reducing pollution by the amount of driving they do. Their argument would be "since we drive less, there's less pollution". Whether they use gasoline or bio-diesel, their approach shouldn't change. They'd simply continue to minimize their driving. This certainly supports the argument that people care about reducing pollution. However, it's a constant - that is, their approach is independent of whether or not bio-diesel fuel is available in cars.

Now, suppose these same drivers continue to use gasoline when bio-diesel is available. Assuming everything else to be the same, the only reason they'd use gasoline is that it's less expensive than bio-diesel. This doesn't mean that they don't care about reducing pollution (they do care, per their minimal driving), but I would argue they don't care as much as the people who are willing to pay 10-20% more for bio-diesel. This, in my estimation, is the critical variable and, therefore, would most strengthen the argument.

Now the big question: what's the true answer?