Which of the following is not a critical aspect of enzyme structure and function? (The structural and functional aspects of enzymes vary widely, but for this question, be sure to focus on critical aspects that apply to virtually all enzymes, and not just specific enzymes.) Choose one: A. Enzyme activity can be switched on and off within cells in order to adjust for changing environmental conditions B. An enzyme displays high affinity and specificity for its substrate. C. Changes in the structure of an enzyme occur after substrate binding due to many (usually) noncovalent interactions. D. A covalent bond forms between an enzyme and substrate following substrate binding.