Question: Biochemical reactions that require high temperatures to proceed are able to take place at body temperature within the cells of living organisms. Which factor is mainly responsible for allowing biochemical reactions to proceed at body temperature?

  Options: 
 A. The cellular enzymes act as catalysts.
 B. The small size of cells keeps reactants together.
 C. The pH of the cytoplasm increases reaction rate.
 D. The reactants are present in small quantities in the cell.
Answer: A