Researchers are increasingly interested in manipulating the environment early in children's lives when they are perceived to be at risk for impoverished intelligence. In a program conducted in North Carolina by Craig Ramey and his associates, pregnant women with IQs averaging 80 were recruited for a study. After their babies were born, half of the infants were cared for during the day at an educational day-care center and half were reared at home by their mothers. Both groups of children were given medical care and dietary supplements, and their families were given social services if they requested them.

At the age of 3, the children who attended the educational day-care center had significantly higher IQs than did the home-reared children. This difference was likely due to the decline in the IQs of the home-reared children during the period from 12 to 18 months of age. By the time the children were 5 years old, 39 percent of the home-reared children had IQs below 85 but only 11 percent of the educational day-care children had IQs this low. In the most recent evaluation of this project, positive effects of educational day-care on the intellectual development and academic achievement of the children were evident at age 12.

Some parents, such as those in Ramey's study, have difficulty providing an adequate environment for the intellectual needs of their infants. Once these difficulties are a recurring part of the family system, changing efforts probably will be more difficult and costly. Early intervention in the family system is directed at changing parental adaptive and responsive functioning so that permanent negative effects are minimized.

In another investigation, the Infant Health and Development Program, early intervention with low birth weight children revealed that both home visitation(探望)and an educational child curriculum improved the children's IQs, decreased behavior. problems, and improved the home environment. The intervention was more effective with mothers with low educational attainment than those with high educational attainment, 'more effective for African-American than White children, and effective for most at- risk children.

Intervention programs have the most positive effects on children's well-being when they (a) begin as early as possible, (b) provide services to parents as well as to the children, (c) have a low child-teacher ratio, (d) have high parental involvement, and (e) have frequent contacts. In one review of family intervention studies, intervention was more effective when there were eleven or more contacts between the intervener and the family. While eleven sessions is a some- what arbitrary number, it does indicate that a certain duration of contact is necessary for intervention success.

From the first sentence we learn that researchers ______.

A．have increased the risks to child growth by manipulating the natural environment

B．are increasingly aware of the effects of environmental factors on intelligence development

C．are increasingly interested in figuring out how intelligence is developed in early child- hood

D．are increasingly interested in manipulating the environment without being aware of the risks involved to children