21. The Crying Game
All normal human infants cry, although they vary a great deal in how much. A mysterious and still unexplained phenomenon is that crying tends to increase in the first few weeks of life, peak in the second or third month, and then decrease. Some babies in the United States cry so much during the peak period-often in excess of three hours a day-and seem so difficult to soothe that parents come to doubt their nurturing skills or begin to fear that their offspring (子孙后代) is suffering from a painful disease. Some mothers discontinue nursing and switch to bottle-feeding because they believe their breast milk is insufficiently nutritious and that their infants are always hungry. In extreme cases, the crying may provoke physical abuse, sometimes even precipitating (使发生) the infant's death.
A look at another culture, the Kung San hunter-gatherers of southern Africa, provides us with an opportunity to see whether care-giving strategies have any effect on infant crying. Both the Kung San and Western infants escalate (使增强) their crying during the early weeks of life, with a similar peak at two or three months. A comparison of Dutch, American, and Kung San infants shows that the number of individual crying episodes are virtually identical. What differs is their length: Kung San infants cry about half as long as Western babies. This implies that care-giving can influence only some aspects of crying, such as duration.
What is particularly striking about child-rearing among the Kung San is that infants are in constant contact with a caregiver; they are carried or held most of the time, are usually in an upright position, and are breast-fed about four times an hour for one to two minutes at a time. Furthermore, the mother almost always responds to the smallest cry or fret (烦躁) within ten seconds.
I believe that crying was adaptive for our ancestors. As seen in the contemporary Kung San, crying probably elicited a quick response, and thus consisted of frequent but relatively short episodes. This pattern helped keep an adult close by to provide adequate nutrition as well as protection from predators. I have also argued that crying helped an infant forge a strong attachment with the mother and-because new pregnancies are delayed by the prolongation of frequent nursing-secure more of her care-giving resources.
In the United States, where the threat of predation has receded (降低) and adequate nutrition is usually available even without breast-feeding, crying may be less adaptive. In any case, care-giving in the United States may be viewed as a cultural experiment in which the infant is relatively more separated-and separable-from the mother, both in terms of frequency of contact and actual distance.
The Western strategy is advantageous when the mother's employment outside of the home and away from the baby is necessary to sustain family resources. But the trade-off seems to be an increase in the length of crying bouts. (490 words)(10分)

21.1  Why does Western infants' crying tend to increase in the first few weeks of life and peak in the second or third month?____(2分)
A. The infants suffer from a painful disease.
B. Their parents lack nurturing skill.
C. The reason is still unknown.
D. Their parents abuse the infants physically.