The critical period is the process the body goes through when quitting drugs often referring to the development of an unborn baby something that even sparrows experience an important window of time for development

An important period of time for development.

Explanation:

In psychology, the critical period can be defined as the period in which some sort of transformation takes place in a limited time. The critical period is that phase of life which is important for the development of certain skills psychologically. This period is also necessary for the development of an organism so that it can progress in a normal manner.

It is the period during which the sensitivity of the nervous system is high. The critical period is also known as the optimal or the sensitive period.

So, the correct answer is the last option.

d.) continue to rise rapidly