The correct answer is D. Coal.
The Grey Revolution is a term used to describe the shift from traditional agriculture to industrial agriculture. This shift has been driven by the need to increase food production to meet the demands of a growing population. Industrial agriculture relies on the use of fossil fuels, such as coal, to power machinery and to produce fertilizers and pesticides. The use of these chemicals has had a negative impact on the environment, leading to soil erosion, water pollution, and climate change.
The other options are incorrect because they are not associated with the Grey Revolution. Orange is a fruit, sand is a type of sediment, and wool is a type of fiber. None of these materials are used in industrial agriculture.
The Grey Revolution has had a significant impact on the world. It has led to an increase in food production, but it has also had a negative impact on the environment. The challenge for the future is to find ways to produce food more sustainably.