What are the reactants of enzyme-catalyzed reactions called?

substrates.

Explanation:

Substrates bind to a part of an enzyme called the active site and remain bound to the enzyme until the reaction is complete, when the products are released. Temperature, pH, and regulatory molecules can affect the activity of enzymes.

the answer is a or when it says crossing over

i think the miocene epoch spans the time from 23 million to 12 million years ago.