Concept:A critical period is a specific time window in early life when the brain is especially receptive to learning a language.
Explanation:Language acquisition is easiest and most natural during this period, which runs from early infancy to puberty.
During this time, children can achieve native‑like fluency and mastery with relative ease.
After the critical period ends, learning a new language becomes much more difficult and less effective.
Thus, the critical period is defined as the phase when language can be acquired with greater ease than at any other time.
Answer:Option A: the period during which language can be acquired with greater ease than any other time.