Explanation:

The Khasi Hills, particularly locations like Mawsynram and Cherrapunji in Meghalaya, receive exceptionally heavy rainfall early in the monsoon season. Their unique funnel-shaped topography traps moisture-laden winds from the Bay of Bengal, leading to intense precipitation. Therefore, option B is correct. Option A, the Western Ghats, also receive heavy rainfall during the monsoon, but the Khasi Hills are renowned for receiving the highest rainfall in India and globally. Option C, the Ganga Valley, receives moderate to heavy rainfall later in the monsoon season. Option D, the Deccan Plateau, lies in the rain shadow of the Western Ghats and generally receives comparatively less rainfall. Thus, A, C, and D are incorrect as they do not experience the earliest and heaviest rainfall to the extent of the Khasi Hills.