The correct answer is: A. A control measure to prevent water pollution.
Root zone processes are a type of wastewater treatment system that uses plants to remove pollutants from the water. The plants absorb the pollutants through their roots, and the clean water is then released back into the environment. Root zone processes are a sustainable and effective way to treat wastewater, and they can be used in a variety of settings, including homes, businesses, and farms.
Option B is incorrect because root zone processes do not involve the spread of plant roots on the ground. Instead, the plants are grown in a specific area, such as a bed or a container.
Option C is incorrect because root zone processes are not designed to prevent soil pollution. However, they can help to improve soil quality by adding nutrients and organic matter.
Option D is incorrect because root zone processes are a type of wastewater treatment system.