Explanation:

Here are some friends of the Indian monsoon which are responsible for its existence and good performance over the years.

• The southwest monsoon derives its name from winds which blow from a south-westerly direction in the Indian subcontinent. We often read about “southwest winds” in various news reports or weather forecasts. But rarely do we think about the "source" of these winds. 
• These come from a powerhouse located more than 4,000 kilometres from India. This powerhouse is known as the Mascarene High. This high-pressure region is located between 25°S-35°S and 40°E-90°E near the Mascarene Islands in the southern Indian Ocean. 
• Coriolis Force is a pseudo force which exists only because of the Earth’s rotational effect. Rotational motion observed in a tropical cyclone is also due to this force. Hence, these monsoon winds get deflected eastwards and now they blow from south-west to the north-east direction. They split into two branches—the Arabian Sea branch and the Bay of Bengal branch.
• El Nino Southern Oscillation (ENSO) refers to the oscillatory mode of the sea surface temperatures near the equatorial Pacific Ocean in which a warming (El Nino or cooling (La Nina) or neutrality is observed. Due to its mostly unpredictable nature, ENSO has been a big challenge for forecasters since a long time. Even trusted models have failed many a time.
• Like ENSO, IOD also has three phases—positive, negative and neutral. During the positive phase of IOD, sea surface temperatures are warmer in the western Indian Ocean (which gives a boost to monsoon winds) as compared to the eastern Indian Ocean—hence a dipole nature.
• The reverse happens during IOD negative and no gradient is observed during the IOD neutral period. It has been observed that during the period of positive IOD, the Indian summer monsoon rainfall is considerably good as compared to the negative IOD period.
• Compared to the roles of Mascarene High, Coriolis Force, India’s summer season and ENSO, IOD’s role has been discovered recently.

Hence option 4th is correct.