A concept that there is a specific time in an organism's development during which external factors have a unique and irreversible impact is:

A. ethology

B. equifinality

C. critical period

D. zone of proximal development

C. Critical period.

Explanation:

Critical period:

In developmental biology, ciritical period is also known as sensitive period which is defined as a period or stage of maturation in the organism's lifespan in which nervous system is more sensitive to various environmental stimulus. Means, brain cell connections are more receptive to influence from surrounding environmental factors. Our body's many cruical functions including behavior are established during critical period with irreversible impact.