Two recent studies have found that punishment is not the best way to influence behavior. One showed that adults are much more cooperative if they work in a system based on rewards. Researchers at Harvard University in the United States and the Stockholm School of Economics in Sweden did the study. They had about two hundred college students play a version of the game known as the Prisoner's Dilemma. The game is based on the tension   between the interests   of an individual and a group. The students played in groups of four. Each player could win points for the group, so they would all gain equally. But each player could also reward or punish each of the other three players, at a cost to the punisher. Harvard researcher David Rand says the most successful behavior proved to be cooperation. The groups that rewarded it the most earned about twice as much in the game as the groups that rewarded it the least. And the more a group punished itself, the lower its earnings were. The group with the most punishment earned twenty-five percent less than the group with the least punishment. The study appeared last month in the journal Science. The other study involved children. It was presented last month in California at a conference on violence and abuse. Researchers used intelligence tests given to two groups. More than eight hundred children aged two to four the first time they were tested. More than seven hundred children aged five to nine. The two groups were retested four years later, and the study compared the results with the first test. Both groups contained children whose parents used physical punishment and children whose parents did not. The study says the IQs--or intelligence quotients--of the younger children who were not _ were five points higher than those who were. In the older group, the difference was almost three points. Murray Strauss from the University of New Hampshire worked with Mallie Paschall from the Pacific Institute for Research and Evaluation. Professor Strauss has written extensively about physical punishment of children. He says the more they are spanked, the slower their mental development. He also looked at average IQs in other nations and found them lower where spanking was more common. According to the passage, the researchers may agree the best way to influence behavior is  _  .
rewarding good behavior correcting bad behavior punishing badly-behaved children praising well-behaved children
Question: Two recent studies have found that punishment is not the best way to influence behavior. One showed that adults are much more cooperative if they work in a system based on rewards. Researchers at Harvard University in the United States and the Stockholm School of Economics in Sweden did the study. They had about two hundred college students play a version of the game known as the Prisoner's Dilemma. The game is based on the tension   between the interests   of an individual and a group. The students played in groups of four. Each player could win points for the group, so they would all gain equally. But each player could also reward or punish each of the other three players, at a cost to the punisher. Harvard researcher David Rand says the most successful behavior proved to be cooperation. The groups that rewarded it the most earned about twice as much in the game as the groups that rewarded it the least. And the more a group punished itself, the lower its earnings were. The group with the most punishment earned twenty-five percent less than the group with the least punishment. The study appeared last month in the journal Science. The other study involved children. It was presented last month in California at a conference on violence and abuse. Researchers used intelligence tests given to two groups. More than eight hundred children aged two to four the first time they were tested. More than seven hundred children aged five to nine. The two groups were retested four years later, and the study compared the results with the first test. Both groups contained children whose parents used physical punishment and children whose parents did not. The study says the IQs--or intelligence quotients--of the younger children who were not _ were five points higher than those who were. In the older group, the difference was almost three points. Murray Strauss from the University of New Hampshire worked with Mallie Paschall from the Pacific Institute for Research and Evaluation. Professor Strauss has written extensively about physical punishment of children. He says the more they are spanked, the slower their mental development. He also looked at average IQs in other nations and found them lower where spanking was more common. According to the passage, the researchers may agree the best way to influence behavior is  _  .
A. rewarding good behavior
B. correcting bad behavior
C. punishing badly-behaved children
D. praising well-behaved children
Answer: