The correct answer is C. The heaviest rainfall during the summer rainy season falls in northeast India because the mountains cause Monsoon winds from the south to rise and drop moisture as rain.
In the Thar desert in the northern Indian subcontinent, the daytime temperature in summer is very high and the surface air rises in altitude causing a local depression. This is the origin of the circulation that is established with the coasts of the Indian Ocean. The warm, humid air from the sea comes from both the east and the west and converges in the Himalayas. This chain of mountains forces the air to rise and is cooled by the law of ideal gases and moisture condenses in the form of clouds and rain. The constant flow of humid air produces abundant rainfall and can reach up to 10,000 mm of rain per year in some places.
This monsoon, which comes from the southwest, is divided into two branches due to the orography of India. These are: the monsoon of the southwest of the Arabian Sea and that of the Bay of Bengal. The wind first reaches the region of the Ghats Mountains on the coast of the state of Kerala in southwestern India. The circulation of the wind is divided in two: the first branch moves to the north along the western slope of the mountains, while the second one passes through the east side of the Deccan plateau and suffers a foehn effect, which drains it and it produces only light rains and of variable distribution in the Deccan peninsula.
The monsoon wind of this second branch passes through the Bay of Bengal, where it gets wet by the evaporation of the surface of the sea, and then runs towards the mouth of the Ganges and traces the slope of the Himalayas east of the mountains of Burma. This branch of the monsoon carries the rain to the northeast of India, the State of West Bengal, Bangladesh and Burma.
The rise of the monsoon wind is accentuated in this region by the funnel shape of the Ganges delta and the rugged mountains. The monsoon wind, blocked by the mountains, must turn west on the Indo-Gangetic Plain and water it in abundance. Cherrapunji, in the state of Meghalaya, located on the southern slope of the Himalayas, is one of the wettest places on Earth. The humidity contained in the monsoon gradually drains along its path and the northwest of India receives almost nothing of rain, being a very arid region.
This process of development of summer monsoon rains is gradually established in the Indian subcontinent, so the date of its start may vary between March and June depending on the region, and its term, from September to November.
