题目内容：

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-fashioned stomach crunches(仰卧起坐). Some can even cause injury — like the $518.99 Body Shaper-Q8SP, which left electrical burns on some researchers at the University of Wisconsin, La Crosse. Others, like the popular Ab-Doer, typically burn less energy than a gentle walk, according to a study to be published in September by the American Council on Exercise.

The fact is that many Americans don't have the biological makeup to develop an obvious abdominal muscles. They are either unable to get the necessary muscle mass or they can't lose enough fat to make a difference. Even if the underlying muscles are well developed, all it takes to hide it is one-sixteenth of an inch of fat. That's enough to exclude most healthy women as well as plenty of guys who do crunches every day.

So what works best? In its new study, the exercise experts researched on the results of the popular Ab-Doer. A lengthy TV advertisement promises that just 10 minutes a day performing such movements as "Body Boogies" and "Good Mornings" will "help form those muscles the fun and easy way without diets." Steven Loy, professor at California State University, Northridge, tested the promise by measuring the electrical activity produced by the abdominal muscles during three Ab-Doer movements. He and his colleagues then compared the results with those produced during traditional exercises. They determined that the muscles were no more active, and in some cases less so, when exercisers were using the Ab-Doer.

Taking a broader approach, researchers at San Diego State University compared 13 abdominal exercises for their ability to develop the central abdominal muscles. They concluded, in a report published in May, that the most effective exercises kept turning the body and worked the muscles the entire time. Among the winners: the bicycle movements — so called because it looks as if you are riding a bike while lying flat on the floor — and exercises performed on the "Captain's Chair", a product typically found in gyms that helps hold the body in the air while you raise your legs up toward your chest. Researchers suggested that a varied routine of the different exercises could deliver the best results.

1.Which of the following is the most effective in building abdominal muscles?

A．Torso Track.B．Captain's Chair.

C．Ab-Doer.D．Body Shaper-Q8SP.

2.According to the author, it's difficult for many Americans to get visible firm abdominal muscles mainly because ________.

A．how big their muscles will be is determined by birth

B．they change their exercise routine regularly

C．injuries interrupt their exercise frequently

D．they do not put in enough efforts

3.The author convinces the readers by ________.

A．describing successful cases

B．presenting findings of researches

C．offering comments directly from exercisers

D．comparing advertisements of products

4.What's the main purpose of this passage?

A．To sponsor rich healthy lifestyle based on advanced product research.

B．To indicate that diet and exercises are necessary factors for a fit midsection.

C．To promote proven exercise techniques and to advise against false advertisements.

D．To research and develop in order to create the perfect stomach and exercise machine.