Arrange the following river basins in descending order according to their size.
(A) Mahanadi
(B) Godavari
(C) Ganga
(D) Pennar
Choose the correct answer from the options given below:

The correct answer is (C), (B), (A), (D).

To arrange the given river basins in descending order (from largest to smallest) according to their size, we look at the catchment area of each river basin:
1. Ganga River Basin (C): The Ganga basin is the largest river basin in India. Within India, it covers an area of approximately 861,452 km² (with a total basin area of over 1,080,000 km² across countries).
2. Godavari River Basin (B): Often called the 'Dakshin Ganga', it is the second-largest river basin in India and the largest among the peninsular rivers, covering an area of approximately 312,812 km².
3. Mahanadi River Basin (A): This major east-flowing peninsular river has a drainage basin of approximately 141,589 km².
4. Pennar River Basin (D): A smaller peninsular river basin in southern India, it has a catchment area of approximately 55,213 km².

Comparing these basin areas, we get the following descending order:
Ganga (C) > Godavari (B) > Mahanadi (A) > Pennar (D)

Therefore, the correct sequence is (C), (B), (A), (D).