An enzyme was mixed with compounds A and C. The concentration of each compound was monitored over time.
You haven't really specified a question. An enzyme is a protein polypeptide that helps to catalyze a particular chemical reaction. The part of the enzyme the catalyzes the reaction is called the active site. It binds to a substrate, or the reagent (or at least one of the reagents) of the chemical reaction and it helps convert the substrate into the product.
In your case you are mixing an enzyme with two different chemical compounds A and C. One of these compounds is probably the substrate. It's also possible that both compounds are substrates that form a new product. Or one is the substrate and the other is the product formed. Regardless, you could monitor the concentrations of both A and C and see how they change over time. The reagent substrate or substrates will decrease in concentration over time and the product will increase in concentration over time. So monitor the concentration of A and C to see how they change to determine their status in the chemical reaction.