What is the main height-related difference between cloud and fog?

Correct answer: Fog is near ground and clouds are above

Correct answer: C, fog is near the ground and clouds are generally above it. Both fog and clouds consist of tiny suspended water droplets and sometimes ice crystals, so their material is similar. The main difference in this question is position. Fog forms at or very close to Earth’s surface and can reduce visibility for people, vehicles, and aircraft near the ground. Clouds usually form higher in the atmosphere, although their bases may be low. A reverses the relationship, so it is incorrect. B uses “only” incorrectly: fog can occur in many places, and clouds can form over both plains, mountains, and oceans. D is also incorrect because neither fog nor clouds are limited only to the sea. C gives the safe general distinction. A useful warning is that fog may be described as a cloud at ground level, but not every cloud is fog. Memory cue: “fog is the cloud you can stand inside.”