Monsoon is caused by

Answer: Option B

The monsoon is caused by the seasonal reversal of winds.
During summer, landmasses tend to heat up more quickly than oceans, creating a low-pressure area over the land. Meanwhile, oceans retain their relatively cooler temperatures, creating a high-pressure area. This pressure gradient causes winds to blow from the ocean towards the land, bringing moisture-laden air. This is known as the summer monsoon.
In winter, the situation reverses. Landmasses cool down more rapidly than oceans, creating a high-pressure area over the land and a low-pressure area over the ocean. This reversal in pressure causes winds to blow from the land towards the ocean, leading to the winter monsoon.

Option A: Temperature changes
While temperature changes are a factor in monsoon dynamics, the primary cause of the monsoon is the seasonal reversal of winds, not just temperature changes.

Option C: Humidity difference
Humidity difference plays a role in the monsoon, but it's not the primary cause. The direction of the winds, influenced by pressure differences, is the key factor in the monsoon phenomenon.

Option D: Pressure differences
Pressure differences indeed play a crucial role in causing monsoons. The seasonal reversal of winds is a result of pressure differences between landmasses and oceans, leading to the monsoon phenomenon.

Therefore, the correct answer is option B: Seasonal reversal of winds.