单选题 In the U. S. , Straus and his colleague Mallie Paschall of the Pacific Institute for Research and Evaluation, looked at 1,510 children--806 kids ages 2 to 4, and 704 ages 5 to 9--and found that roughly three--quarters had endured some kind of corporal punishment in the previous two weeks, according to interviews with the mothers. Researchers measured the children's IQ initially, then again four years later. Those kids who hadn't been spanked in the initial survey period scored significantly better on intelligence and achievement tests than those who had been hit. Among the 2 - to - 4 - year - olds, the difference in IQ was five points ; among the older kids, there was a 2.8 - point gap. That association held after taking into account parental education, income and other environmental factors, says Straus.
Which group of the children scored better in the survey?

• A. The children who had been spanked often.
• B. The children who had been spanked occasionally'.
• C. The children who had not been spanked.
• D. The children who had been spanked only onc