The Process Called Substrate Cycling Is Used to Describe This

Multiple Choice

The process called substrate cycling is used to describe this process:

A) Freely reversible reactions.
B) Recycling of vitamins as catalysts in metabolism
C) Situations where there are two different enzymes used to reverse a specific step in a metabolic pathway.
D) Metabolic pathways which run in cycles and regenerate the initial molecule.
E) None of these answers describes substrate cycling.