The correct answer is 1, 2, 3 and 4 Key Points The Madden-Julian Oscillation MJO is a moving low-pressure disturbance of clouds that intensifies over three regions - the eastern Indian Ocean, south of the maritime continent, and the western Pacific Ocean and transfers a part of its energy to the underlying ocean. Due to its low-pressure nature, it triggers cyclone formation over the Indian Ocean which results in an increase in temperature and a decrease in pressure which eventually leads to a delay in monsoon. Hence statement 1 is correct. When Cyclones formed on the sea surface, the sea surface gets warmer and the temperate difference between land and sea reduced. This is the major cause of weakening monsoon winds and delaying it. Hence statement 2 is correct. In El Nino sea surface temperature (SST) of the Pacific Ocean rises off the coast of Peru in South America, which reduces the development of high pressure on the Indian ocean and weakens the monsoon. Hence statement 3 is correct. Western disturbances lead to lowering the temperature of landmass for a long time, hence at Tibet plateau low pressure occurs, hence delay in monsoon. Hence statement 3 is correct.