With reference to India, which one of the following statements is not correct?
(a) About one-third of the area of the country records more than 750 millimetres of annual rainfall.
(b) The dominant source of irrigation in the country is wells
(c) Alluvial soil is the predominant type of soil in the northern plains of the country
(d) The mountain areas account for about thirty percent of the surface area of the country
