Answer:
a. sensitization
Step-by-step explanation:
Sensitization: In psychology, the term sensitization is defined as a non-associative learning procedure in which a person after getting repeated exposure to a specific stimulus can develop progressive amplification i.e the increased strength towards the stimulus-response or reaction. Through sensitization, a person might react to something that formerly did not affect the person.
In the question above, sensitization has come over to the normal reaction to sirens.