Answer:
Cellular respiration involves many reactions in which electrons are passed from one molecule to another. Reactions involving electron transfers are known as oxidation-reduction reactions (or redox reactions).
An asteroid hitting the earth would cause a lot of dust, ash, and other debris to go into the atmosphere which would block the sun which would cause the temperature to decrease.
I think it is A but not 100% sure. Think of an enzyme like a key unlock the lock is the protein. And to activate getting inside your car or house you have to fit the key into the lock.