The correct answer is: a) East Khasi Hills.
East Khasi Hills is the most populous district in Meghalaya, with a population of 2,418,682 as of 2011. It is located in the central part of the state and is the largest district in terms of area. The district is home to the capital city of Shillong, as well as several other important towns and villages. The main language spoken in East Khasi Hills is Khasi.
The other options are incorrect because they are not the most populous districts in Meghalaya. West Garo Hills has a population of 1,459,067, Ri Bhoi has a population of 462,962, and South West Khasi Hills has a population of 367,312.
East Khasi Hills is a beautiful and diverse district with a rich history and culture. It is a popular tourist destination, and is home to several important historical and cultural sites. The district is also home to a number of important industries, including agriculture, tourism, and manufacturing.