The correct answer is D. Fallow land.
Culturable commanded area (CCA) is the gross area of an irrigation canal system that can be cultivated. It is calculated by subtracting the area that is not suitable for cultivation, such as populated areas, alkaline areas, and forest areas, from the total area of the canal system.
Fallow land is land that is not being cultivated. It may be left fallow for a number of reasons, such as to allow the soil to recover, to rotate crops, or to raise livestock. Fallow land is not included in the calculation of CCA because it is not being used for cultivation.
A. Populated area is not suitable for cultivation because it is occupied by buildings and other infrastructure.
B. Alkaline area is not suitable for cultivation because the high pH level of the soil makes it difficult for plants to grow.
C. Forest area is not suitable for cultivation because the trees and other vegetation prevent the growth of crops.