Answer:
Option C is correct: a hydrogen fuel cell has a low environmental impact if produced from water.
Option A is incorrect because hydrogen fuel cells do not require hot spots and can be used anywhere.
Option B is incorrect because while hydrogen fuel cells are used as a fuel for some cars, they are not yet widely used.
Option D is partially incorrect. Hydrogen fuel cells are expensive, but they do not leak radiation. However, there are some safety concerns with the handling and storage of hydrogen fuel.