What is aerobic respiration? (put simply)

Aerobic respiration is the process of producing cellular energy involving oxygen. Cells break down food in the mitochondria in a long, multistep process that produces roughly 36 ATP. The first step in is glycolysis, the second is the citric acid cycle and the third is the electron transport system.

The correct option is D) The products of the reaction are released from the active sites of the enzyme, allowing other substrate molecules to bind with the sites. 

Enzymes are protein molecules which have a specific shape complimentary to the substance they act on, known as the substrate. The region where the reaction occurs is the enzyme's active site. However, when the reaction is complete, the products leave the active site and the enzyme is once again available for reaction. This means that the enzyme is unchanged through the reaction. This is why enzymes are known as biological catalysts.