Which statement about enzymes is true? An enzyme functions to increase the activation energy in a reacton.
Enzymes are proteins that function as catalysts in nonliving things.
Each enzyme can catalyze many different biochemical reactions.
Enzymes and substrates fit together like a lock and key.

Enzymes and substrates fit together like a lock and key since, in one enzymatic reaction, only the correct substrate (i.e., the key) binds to its corresponding enzyme (i.e. the lock).  

Explanation:

An enzyme (or catalyst) is one protein that has catalytic functions, being therefore capable of accelerating chemical reactions. The enzymes are known to control the rate of these chemical reactions (i.e., catalysis) without suffering alterations during these processes. Thus, the enzymes are proteins that catalyze chemical reactions that are not favored under normal conditions. Moreover, one enzyme may catalyze more than one chemical transformation, as well as the same reaction may be catalyzed by two or more enzymes.

the sea slugs belong to the same class