Question

the lock - and - key mechanism refers to
the complementary shapes of an enzyme and a substrate.
the attractive forces between an enzyme and a substrate.
the ability of an enzyme to lower the activation energy of a reaction.
the ability of an enzyme to \unlock\ the products of a reaction.

Explanation:

The lock - and - key model describes how an enzyme's active site has a specific shape that fits the substrate's shape like a lock and key.

Answer:

the complementary shapes of an enzyme and a substrate.