Pretty sure the answer is A
Energy from a source that is not depleted when used, such as wind or solar power.
You cant settle in deserts due to lack of water and scarcity of food, which led to the Saharan regions being less populated. Hope this helps.
Low dissolved oxygen concentrations that occur in many bodies of water when nutrients stimulate the growth of algae that subsequently die and are decomposed by oxygen-using bacteria.
Quality inputs (improved seeds and fertilizers) are essential to raising productivity (yields per unit area planted) under both the rainfed and irrigated conditions. In addition, strong extension and advisory services are important for enhancing the adoption and efficiency of improved inputs.
