The correct answer is A. Pressure difference.
The monsoon is a seasonal reversal of wind direction between the northern and southern hemispheres. It is caused by the difference in temperature between the land and the ocean. In the summer, the land heats up faster than the ocean, causing the air to rise. This creates an area of low pressure over the land. The air from the ocean, which is cooler and at higher pressure, then flows in to fill the low-pressure area. This is the monsoon wind.
The monsoon winds are strongest in the Indian subcontinent, where they bring heavy rains. The rains are essential for the region’s agriculture.
Option B, nearness to sea, is not the main cause of the arrival of monsoon in Bihar. The monsoon winds are caused by the difference in temperature between the land and the ocean, not by the nearness of the land to the sea.
Option C, nearness to Himalayas, is also not the main cause of the arrival of monsoon in Bihar. The Himalayas do not affect the monsoon winds. The monsoon winds are caused by the difference in temperature between the land and the ocean, not by the nearness of the land to the Himalayas.
Option D, none of the above, is also not the correct answer. The main cause of the arrival of monsoon in Bihar is pressure difference.