题目

  We’ve all seen them: perfectly toned famous people on late-night television telling us that we too can develop rock-hard abdominal muscles(腹部的). It's easy! Just pay $149.99 for the Torso Track or $149.75 for the Ad-Doer and watch those unwanted inches leave your waist. Americans spend tens of millions of dollars on various products to firm up their fat around the waist.   And did they work? Not necessarily. Independent studies have concluded that most of these products ---- no matter who approved them or how expensive they are ---- shape your midsection no better than old-f下列生物中不属于单细胞生物的是（　　） A、变形虫B、玉米C、草履虫D、衣藻