题目内容：
根据下面材料，回答题。Exercise Lowers Employers' Health Costs
Companies can save millions in health-care costs simply by encouraging their employees to exercise a little bit, researchers reported on Friday.
They said obese (肥胖的) employees had higher health-care costs, but lowered those expenses by exercising just a couple of times a week, without even losing any weight.
Feifei Wang and colleagues at the University of Michigan studied 23,500 workers at General Motors.
They estimated that getting the most sedentary (惯于久坐的) obese workers to exercise would have saved about $790,000 a year, or about 1.5 percent of health-care costs for the whole group,Company-wide. The potential savings could reach $7.1 million per year, they reported in the Journal of Occupational and Environmental Medicine.
Of the whole group of workers, about 30 percent were of normal weight,45 percent were overweight (超重的), and 25 percent were obese. Annual health-care costs averaged $2,200 for normal weight, $2,400 for the overweight, and $2,700 for obese employees.
But among workers who did no exercise, health-care costs went up by at least $100 a year, and were $3,000 a year for obese employees who were sedentary.
But adding two or more days of light exercise, at least 20 minutes of exercise or workhard enough to increase heart rate and breathing, lowered costs by on average $500 per employee a year, the researchers found.
"This indicates that physical activity behavior could reduce at least some of the harmful effects of excess body fat, and in consequence, help lower the health-care costs," Wang and colleagues wrote.
How can employees help lower the health-care costs? A．By taking more rest.
B．By eating less.
C．By exercising a little bit.
D．By saving more money.
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