The correct answer is D) extensive snowfall. In polar regions, you would expect to see extensive snowfall, not the absence of it. The other options - false horizons, mirage effects, and sea smoke - are all common phenomena that can be observed in polar regions due to the unique environmental conditions. False horizons and mirage effects are caused by the refraction of light due to temperature inversions, which are prevalent in polar regions. Sea smoke is formed when cold air passes over relatively warmer water, which is also a common occurrence in polar environments. However, extensive snowfall is an expected and characteristic feature of polar regions.