The correct answer is D. They work on a single set of substrates.
Enzymes are highly specific and typically catalyze reactions for a particular substrate or a group of closely related substrates. The other options are not true for all enzymes:
A. While many enzymes are specific to certain reactions, some enzymes (like multifunctional enzymes) can catalyze more than one type of reaction, so this statement is not universally true.
B. Enzymes do not change the amount of energy released at the end of a reaction; they lower the activation energy required to initiate the reaction but do not alter the overall energy change of the reaction.
C. Enzymes are not necessarily broken down or inactivated immediately following the reactions they catalyze; many enzymes can be reused multiple times.
Therefore, D is the most accurate statement that applies to all enzymes.