The correct answer is C. Pleasant and dry weather.
Winter in Karnataka is mild with pleasant and dry weather. The average temperature in Bangalore during winter is around 20 degrees Celsius. The days are sunny and warm, while the nights are cool and pleasant. There is very little rainfall during winter, and the humidity is low. This makes it a good time to visit the state, as you can enjoy the outdoors without the heat and humidity of the summer months.
Option A is incorrect because frost is not common in Karnataka during winter. Option B is incorrect because sub-zero temperatures are also not common in Karnataka during winter. Option D is incorrect because heavy fog is not common in Karnataka during winter.