Question

the concept that enzymes and substrate fit perfectly with each other
enzyme
lock & key
names of enzymes
factors that affect enzyme activity

Explanation:

The "Lock & Key" model in enzyme - substrate interaction proposes that the enzyme (lock) and substrate (key) have complementary shapes that fit perfectly together, which matches the described concept. The other options: "Enzyme" is a general term for the biological catalyst, not the concept of fitting; "Names of Enzymes" are just labels for different enzymes; "Factors that affect Enzyme Activity" are things like temperature, pH, etc., that influence how enzymes work, not the fitting concept.

Answer:

B. Lock & Key