B. explain that customers won't change their buying habits completely

C. show his fear that chicken or pork may be an alternative to beef

D. indicate that ranchers may be least affected by the high beef prices

Your New Year's plan to move more is one of the toughest to stick to, and a group of scientists working with obsess（过度肥胖的）mice think they're starting to understand why.

Rather than our sedentary(久坐的) lives causing weight gain, says Alexxai Kraviz, the National Institutes of Health neuroscientist who led the study, changes in brain chemistry after we start gaining weight affect our capacity to move.

"Obese mice can move just fine," says Kravitz, who published the work with his team in Cell Metabolism "They just don't."

What Kravitz's team found is that the activity of a particular dopamine(多巴胺) receptor linked to movement goes down as mice gain weight on a high-fat diet. So the mice slow down and they move less. And when the researchers restored the activity of that dopamine receptor-DR2-the mice started moving more, even though they were still obese. The team also saw that lean mice missing the DR2 receptor acted like obese mice. This is the target, says Kravitz-restoring that dopamine receptor function. "Maybe 20 or 30 years down the road, we could do that in people," he says.

And there is one more thing: The scientists fed normal mice and the mice lacking DR2 the same high-fat diet. Both sets of mice gained weight at the same rate.

Kravitz says this is important because mice lacking DR2 move less from the get-go, whereas a normal mouse takes a little time to start seeing that dopamine receptor-related loss of exercise. The ability to exercise seems to be disconnected from weight gain, he says.

"Exercise is a healthy things to do, but its impact on weight loss has been exaggerated," he says. "We have to be realistic about the size of the effect of exercise on weight, as opposed to health benefits."

Still, before you abandon your New Year's exercise plan, keep in mind that this study was done using a high-fat diet, and not the normal calorie restriction that people maintain when they diet. That's a big drawback to the work, says Vicki Vieira-potter, a University of Missouri physiologist not involved in the study.

"They feed the mice with high-fat diet, it damages the receptor, and that decreases activity. Those who plan to lose weight should remember a high-fat diet is a mice way to cause obesity in the lab, but it's not the same as the normal situation of obesity," she says.

She also says that a lot of the weight gain in the mice came after they stopped moving around, which indicates that the loss of movement did impact obesity.

7. Alexxai Kravitz is likely to agree that_______.

A. high-fat food lead to the lack of DR2

B. less movement results from weight gain

C. weight gain leads to the inactivity of DR2

D. the lack of DR2 results in less movement

8. What can we infer from the research mentioned in the passage?

A. High-fat diet is bound to cause obesity

B. High-fat diet has little influence on the rate of weight gain

C. The research team aim to deal with human obesity