Concept:Farming is the activity of growing plants and raising animals for food and other products. Its main output is the products obtained from this activity.Explanation:The options are air, crops, water, and machines. Air and water are natural resources needed for farming, not outputs. Machines are tools used in farming. Crops are plants grown and harvested, such as grains, vegetables, or fruits. These are directly produced by farming and are sold or consumed. Therefore, crops are the correct output.Answer:Crops (Option B)