Given that ATP is the product of the reaction, it must be cellular respiration (also, since it occurs in both plants and animals it can't be photosynthesis).
A and B must be glucose and oxygen. It makes sense if you think about it. We breathe in oxygen, and we eat food. Food contains glucose (sugar). We need to consume these things in order to make energy. Carbon dioxide is D because it's the "left over" of this reaction. That's why we exhale it. And C is enzymes because they catalyze (promote) just about every reaction in the body.
Another way to remember this in the future is just to memorize the equation (attached). Just remember that its the exact opposite of photosynthesis.
