The correct option is "many" because "many" refers to a large number of parts, which is suitable in this context. The sentence is referring to multiple areas or sections of the world, and "many" appropriately describes the quantity of these parts.
Thus, the correct sentence is: "Clean water is a precious commodity in many parts of the world."
Arun’s present age in years is 40% of Barun’s. In another few years, Arun’s age will be half of Barun’s. By what percentage will Barun’s age increase during this period?