The classical study of family size and IQ was conducted in the Netherlands. It was based on the military examinations of more than 386,000 Dutchmen. Researchers found that the brightest subjects came from the smallest families and had few, if any, brothers and sisters when they were born. Thus the firstborn child in a family of two was usually brighter than the last child in a family.

The effects of family size on intelligence may be explained by what a house full of children does to the home environment. It increases the amount of time a child spends with other children and decreases the amount of parental attention he or she receives. For example, a parent with one restless child is likely to sit and play with the child. The same parent with two or three restless children is more likely to ask them to play with each other. Some psychologists say that when a child interacts with an adult alone, the child learns more and therefore intelligence is increased. Researchers have also found that parents often expect more from their firstborn, which motivates such children to seek a higher standard.

Not all psychologists agree that firstborns tend to be more intelligent. They say that the data need to be examined more closely for other possible explanations. For example, in industrialized nations most large families come from lower socio-economic backgrounds. Thus environment, not family size or birth order, may be influencing intelligence. On the other hand, there may be genetic variations (基因变异) within families that also explain the cause of differences.

If firstborns have advantages in the area of intelligence, research has also shown that they may be more conforming (墨守成规) and have poorer social skills than their younger siblings (brothers and sisters ). Although more research needs to be done in this area, it is clear that such factors as birth order, the order in which boys and girls are born into a family, the number of years that separate siblings probably have an effect on the development of intelligence, personality, and social relationships.

60.   The underlined word "subjects" in the first paragraph means ________.

A. branches of knowledge                                        B. persons chosen to be studied in experiments

C. any member of a state except the top ruler   D. something to be considered

61.   Psychologists are divided with regard to (关于) their opinions toward________.

A. the way in which the data are explained       B. the advantages of firstborns in the area of IQ

C. the planned size of families                 D. the factors influencing intelligence

62.   Why are firstborns encouraged to seek a higher standard?

A. They are more obedient (服从) and have poorer social skills.

B. Their parents spend less time with other children.

C. They obtain more attention from their parents.

D. Their parents expect more from them.

63.   The best title for this passage would be________.

A. Family Size and IQ                         B. The Preference of Boys to Girls

C. The Development of Intelligence               D. Factors Influencing IQ