Answer: D
Explanation: The experiment was set up using the very same species of yeast labeled differently. What this means is that they are of the same type or kind and thus would exhibit similar features from feeding to the metabolism of the food they take and subsequent production of by-products of the fermentation process. In this regard, therefore, the reasonable conclusion that can be drawn regarding these cultures is that both cultures A and B are synthesizing the same amount of ATP per unit of glucose in glycolysis (the cellular degradation of the simple sugar glucose to yield pyruvic acid, and ATP as an energy source).