Answer:
(A) runs from the second month after birth to the end of lactation, usually by the end of the third year.
Step-by-step explanation:
Infancy, among humans, the period of life between birth and the acquisition of language approximately one to two years later.
The average newborn infant weighs 3.4 kg (7.5 pounds) and is about 51 cm (20 inches) long. The newborn gains weight at an average of 170 to 200 g (6 to 7 ounces) per week for the first three months. Growth continues, but the rate gradually declines to an average of 60 g per week after 12 months.
Newborns typically sleep for about 16–18 hours a day, but the total amount of time spent sleeping gradually decreases to about 9–12 hours a day by age two years. At birth infants display a set of inherited reflexes involving such acts as sucking, blinking, grasping, and limb withdrawal. Infants’ vision improves from 20/800 (in Snellen notation) among two-week-olds to 20/70 vision in five-month-olds to 20/20 at five years. Even newborns are sensitive to certain visual patterns, chiefly movement and light-dark contrasts and show a noticeable preference for gazing at the human face; by the first or second month they can discriminate between different faces, and by the third they can identify their mother by sight. Young infants also show a predilection for the tones of their mother’s voice, and they manifest a surprising sensitivity to the tones, rhythmic flow, and sounds that together make up human speech.
The ideal food for the young infant is human milk, though infant formula is an adequate substitute. Babies can usually be weaned after they are six months old, and the appearance of teeth allows them to switch from soft foods to coarser ones by the end of the first year. The first tooth usually erupts at about six months. By the end of the first year, six teeth usually have erupted—four upper incisors and two lower incisors.