Thinner isn’t always better.A number of studies have 1_that normal-weight people are in fact at higher risk of some diseases compared to those who are overweight.And there are health conditions for which being overweight is actually_2_.For example,heavier women are less likely to develop calcium deficiency than thin women.3 among the elderly,being somewhat overweight is often an_4 of good health.Of even greater 5 is the fact that obesity turns out to be very difficult to define.It is often defined 6_body mass index,or BMI.BMI 7 body mass divided by the square of height.An adult with a BMI of 18 to 25 is often considered to be normal weight.Between 25 and 30 is overweight.And over 30 is considered obese.Obesity,8,can be divided into moderately obese,severely obese,and very severely obese.While such numerical standards seem 9,they are not.Obesity is probably less a matter of weight than body fat.Some people with a high BMI are in fact extremely fit,10 others with a low BMI may be in poor 11.For example,many collegiate and professional football players 12 as obese,though their percentage body fat is low.Conversely,someone with a small frame may have high body fat but a 13 BMI.Today we have a（an）_14_to label obesity as a disgrace.The overweight are sometimes_15_in the media with their faces covered.Stereotypes_16_with obesity include laziness,lack of will power,and lower prospects for success.Teachers,employers,and health professionals have been shown to harbor biases against the obese._17_very young children tend to look down on the overweight,and teasing about body build has long been a problem in schools.Negative attitudes toward obesity,_18_in health concerns,have stimulated a number of anti-obesity_19_.My own hospital system has banned sugary drinks from its facilities.Many employers have instituted weight loss and fitness initiatives.Michelle Obama launched a high-visibility campaign_20_childhood obesity,even claiming that it represents our greatest national security threat.10选？

A. so

B. while

C. since

D. unless