We all know that eating junk food can make us fat. However, a new study suggests that it can do more than that - it can also make us lazy, reported CBS News. In the study, researchers at the University of California, Los Angeles, US divided 32 female rats into two groups. The first group was fed a diet of healthy food such as corn and fish, while the second was given a diet of highly processed   food rich in sugar, namely "junk food". Within three months, the rats in the second group were already much fatter than those on the healthy diet. And when researchers trained the rats to do simple tasks, they found even more differences between the two groups rather than weight. During the task - pushing a lever   to receive a reward of sugar water - the rats on the junk food diet were found to be less willing to move, and they took longer breaks between each push than the lean rats did. "It is as if the rat is thinking 'This is too much work'," Aaron Blaisdell, leader of the study, told the Los Angeles Times. But what about the possibility that the fat rats were less passionate about getting sugar water because they were already eating lots of sugar in their daily diet? That's why researchers repeated the tests by rewarding fat rats with plain water when they were extremely thirsty. However, the results came out just the same. According to researchers, these differences suggest that junk food changed the chemistry in the rats' brains. The experiment didn't end _ . After six months, the rats' diets were switched, and the overweight rats were given a healthy diet for nine days. However, this change didn't help reduce their weight or improve their ability to perform tasks, which means the effects of their junk food diet persisted  . "There's no quick fix," said Blaisdell. For a long time, we've believed that people become fat because they are lazy. But this study has proven the opposite to be true as well, which indicates that laziness and obesity are a "vicious cycle  ". So, if you constantly feel tired, lacking any urge to get up from your chair, it could be that you've been studying too hard. But you should also pay attention to your diet. The researchers rewarded thirsty rats with plain water in the lever test to   _  .
help them control their weight test whether fat rats lost interest in the test because they had taken enough sugar change the diet habits of fat rats find out the influence of sugar on rats' brains
Question: We all know that eating junk food can make us fat. However, a new study suggests that it can do more than that - it can also make us lazy, reported CBS News. In the study, researchers at the University of California, Los Angeles, US divided 32 female rats into two groups. The first group was fed a diet of healthy food such as corn and fish, while the second was given a diet of highly processed   food rich in sugar, namely "junk food". Within three months, the rats in the second group were already much fatter than those on the healthy diet. And when researchers trained the rats to do simple tasks, they found even more differences between the two groups rather than weight. During the task - pushing a lever   to receive a reward of sugar water - the rats on the junk food diet were found to be less willing to move, and they took longer breaks between each push than the lean rats did. "It is as if the rat is thinking 'This is too much work'," Aaron Blaisdell, leader of the study, told the Los Angeles Times. But what about the possibility that the fat rats were less passionate about getting sugar water because they were already eating lots of sugar in their daily diet? That's why researchers repeated the tests by rewarding fat rats with plain water when they were extremely thirsty. However, the results came out just the same. According to researchers, these differences suggest that junk food changed the chemistry in the rats' brains. The experiment didn't end _ . After six months, the rats' diets were switched, and the overweight rats were given a healthy diet for nine days. However, this change didn't help reduce their weight or improve their ability to perform tasks, which means the effects of their junk food diet persisted  . "There's no quick fix," said Blaisdell. For a long time, we've believed that people become fat because they are lazy. But this study has proven the opposite to be true as well, which indicates that laziness and obesity are a "vicious cycle  ". So, if you constantly feel tired, lacking any urge to get up from your chair, it could be that you've been studying too hard. But you should also pay attention to your diet. The researchers rewarded thirsty rats with plain water in the lever test to   _  .
A. help them control their weight
B. test whether fat rats lost interest in the test because they had taken enough sugar
C. change the diet habits of fat rats
D. find out the influence of sugar on rats' brains
Answer: