单选题 《复合题被拆开情况》 We didn’t worry much about keeping fit 100 years ago. A sizeable percentage of the world’s population was reaping and sowing, herding and mowing its way through life on preindustrial farms. In coastal cities, strong-shouldered stevedores (码头搬运工) were loading and unloading ships dawn to dusk without a container in sight. Builders and railroad men drove nails or sawed wood using muscles, not power tools. And for those doing the washing, cooking and scrubbing at home, life wasn’t so dainty (文雅的) either. In that bygone, sweat-drenched era, staying in shape just wasn’t an issue. Working out? Never heard of it. Literally, the old energy-balance equation—calories in should equal calories out—is seriously out of order, as the rising rates of obesity in the developed world prove. For much of the past decade, health professionals and the popular press have focused on the intake side of the equation. We’re eating too much fat, too many carbs (含碳水化合物的食物), too much altogether. But the problem is just as grave on the output side. We are not burning enough calories or moving our bodies enough to maintain good health. "We have two epidemics in America. One is obesity, the other is physical inactivity," remarks Dr. Tim Church. How does exercise help us? To begin with, it works wonders for the heart: reducing the risk of heart disease and restoring function after a heart attack. In addition, it can help to moderate blood pressure in people with hypertension, significantly relieve depression and anxiety, and maintain cognitive function in old age. Studies show that physical activity may also assist in preventing certain cancer. The World Health Organization estimates that physical inactivity is responsible for 1.9 million deaths every year. In the U. S. , a third of adults are obese, and a quarter of them admit that they spend virtually no leisure time on exercise. A recent study by the University of Hong Kong found that lack of physical activity was linked to one in five deaths in the city. Another study found that long working hours and lack of exercise had left citizens of Hong Kong in their 20s and 30s with the breathing capacities of men and women years older.《问题》：What kind of issue have health professionals focused on in the past decade?