Answer:
The correct answer is B.. The enzyme is like a lock, and the substrate is like a key.
Enzymes are bioctalyst which accelerate the bio-chemical reactions taking place inside the living organisms.
Enzymes have specific region in their structure for the binding of their substrate which is called as active site. The shape of the active site of the enzyme complements the shape of the substrate.
The shape and amino acid residues of the active site provide the specificity to the enzyme for its substrate.
It can be easily explained with the help of lock and key model in which a substrate (key) perfectly docks in the active site (key hole) of the enzyme (the lock).
