Why is it most correct to call fog a cloud near the ground?

Correct answer: Because it is made of suspended tiny droplets in air near the ground

Correct answer: A. Fog is essentially a cloud whose tiny water droplets are suspended in the air close to the ground. First, moist air cools until it reaches its dew point, or saturation point. Water vapour then condenses on very small particles such as dust or smoke and forms microscopic liquid droplets. When these droplets remain near the surface, we call the visible layer fog; when a similar layer is at a higher altitude, we call it a cloud. A is correct because it describes both the droplets and their low height. B is wrong because dust alone is not fog, although dust may provide condensation nuclei. C is wrong because fog can form at many elevations, not only below sea level. D is wrong because fog contains condensed water droplets, not vapour-free air. Memory cue: a cloud touching or lying close to the ground is fog; height, not a completely different substance, is the main distinction.