Concept of critical period assumes :

Correct option is A

(a) irreversible damage in course of development.
The concept of a critical period in development suggests that there are specific times in an individual's life when certain experiences have a profound impact. This concept implies that if these experiences do not occur during these specific periods, the individual may experience irreversible damage or fail to develop certain abilities. This idea is most prominently discussed in language acquisition and sensory development.