Use this fact to answer the question: fog is formed by water vapor condensing in the air

If a high percentage of water is visible in the air?

Select from:
[a]. this is called heat and it is unsafe to drive in
[b]. this is called fog and it is safe to drive in
[c]. this is called heat and is safe to drive in
[d]. this is called fog and is unsafe to drive in

The answer is:
[d].