The correct answer is: a) Summer monsoon.
The summer monsoon is a seasonal wind pattern that brings heavy rains to much of South Asia, including Mizoram. The monsoon is caused by the difference in temperature between the land and the ocean. During the summer, the land heats up faster than the ocean, creating an area of low pressure over the land. This low pressure draws in moist air from the ocean, which rises and cools, causing the water vapor to condense and fall as rain.
The summer monsoon typically begins in June and lasts until September. The heaviest rains usually fall in July and August. The monsoon is essential for the agriculture of South Asia, as it provides the water needed to grow crops. However, the monsoon can also cause flooding and landslides, which can be destructive.
The other options are incorrect because they are not the seasons that bring heavy rainfall to Mizoram. Winter is the dry season in Mizoram, and spring and autumn are relatively dry seasons as well.