Pakistan has been able to turn millions of acres into rich farmland with

Irrigation from the Indus River

Irrigation and the tube well system.

Explanation:

As agriculture is an important sector in Pakistan and about 26% of the GDP of the nation is depend on it. Farmers mainly use the synthetic chemicals and control pests and the major crops, including the wheat, rice, the sugarcane, and maize and cotton has significant importance with the agricultural system of Pakistan.The irrigation system was developed by the Indus valley civilization and that led to the drainage and the sewage system of the country. About 25% of the water is withdrawn for the agriculture sector and is essential for the maintain a rich farmland.

The answer is d if you are on edgenuity. 

Why you put last one a? i think is b.