Which of the following are the main reasons for the origin of the south-west monsoon in India?
I. Development of a low pressure in north-west India
II. Deflection of trade winds
III. Arrival of cyclonic stream from the Pacific Ocean
IV. Heating of the Arabian Sea and the Bay of Bengal

The main reasons for the origin of the south-west monsoon in India are Development of a low pressure in north-west India and Deflection of trade winds. These winds originate in the Southern Hemisphere, cross the Equator (trade winds) and gets deflected to the right by the Coriolis force in the Northern Hemisphere.