Infancy is the period that:
a. runs from the second month after birth to the end of lactation, usually by the end of the third year.
b. runs from three to seven years, generally postweaning.
c. is also called the "neonatal" period.
d. includes three months before birth and three months after birth.

a. runs from the second month after birth to the end of lactation, usually by the end of the third year.

Explanation:

Infancy peculiar to humans is a period that ranges from birth to the end of lactation, usually by the end of the third year. It is a time of extreme dependence on their mothers and by extension adults. It follows the neonatal period which extends from birth to 30days (1 month).

The infancy period is one of rapid growth and development.