PALO ALTO, California----"Switching off the television may help prevent children from getting fatter---- even if they do not change their diet or increase the amount they exercise," US researchers said last week. A study of 192 third and fourth graders, generally aged eight and nine, found that children who cut the number of hours spent watching television gained nearly two pounds(0.9kg) less over a one-year period than those who did not change their television diet. "The findings are important because they show that weight loss can only be the result of a reduction in television viewing and not any other activity," said Thomas Robinson, a pediatrician  at Stanford University. "American children spend an average of more than four hours per day watching television and videos or playing video games, and rates of childhood being very fat have doubled over the past 20 years," Robinson said. In the study, presented this week to the Pediatric Academic Societies' annual meeting in San Francisco, the researchers persuaded about 100 of the students to reduce their television viewing by one-quarter to one-third. Children watching fewer hours of television showed a significantly smaller increase in waist size and had less body fat than other students who continued their normal television viewing, even though neither group ate a special diet or took part in any extra exercise. "One explanation for the weight loss could be the children unstuck to the television may simply have been moving around more and burning off calories," Robinson said. "Another reason might be due to eating fewer meals in front of the television. Some studies have suggested that eating in front of the TV encourages people to eat more," Robinson said. According to the passage, the time American children usually spend on watching TV  _  .
is more than four hours a day is less than four hours a day doubled in the last twenty years is more than on any other activities
Question: PALO ALTO, California----"Switching off the television may help prevent children from getting fatter---- even if they do not change their diet or increase the amount they exercise," US researchers said last week. A study of 192 third and fourth graders, generally aged eight and nine, found that children who cut the number of hours spent watching television gained nearly two pounds(0.9kg) less over a one-year period than those who did not change their television diet. "The findings are important because they show that weight loss can only be the result of a reduction in television viewing and not any other activity," said Thomas Robinson, a pediatrician  at Stanford University. "American children spend an average of more than four hours per day watching television and videos or playing video games, and rates of childhood being very fat have doubled over the past 20 years," Robinson said. In the study, presented this week to the Pediatric Academic Societies' annual meeting in San Francisco, the researchers persuaded about 100 of the students to reduce their television viewing by one-quarter to one-third. Children watching fewer hours of television showed a significantly smaller increase in waist size and had less body fat than other students who continued their normal television viewing, even though neither group ate a special diet or took part in any extra exercise. "One explanation for the weight loss could be the children unstuck to the television may simply have been moving around more and burning off calories," Robinson said. "Another reason might be due to eating fewer meals in front of the television. Some studies have suggested that eating in front of the TV encourages people to eat more," Robinson said. According to the passage, the time American children usually spend on watching TV  _  .
A. is more than four hours a day
B. is less than four hours a day
C. doubled in the last twenty years
D. is more than on any other activities
Answer: