173. Researchers have found that when very overweight people, who tend to have relatively low metabolic rates, lose weight primarily through dieting, their metabolisms generally remain unchanged. They will thus burn significantly fewer calories at the new weight than do people whose weight is normally at that level. Such newly thin persons will, therefore, ultimately regain weight until their body size again matches their metabolic rate.

The conclusion of the argument above depends on which of the following assumptions?

(A) Relatively few very overweight people who have dieted down to a new weight tend to continue to consume substantially fewer calories than do people whose normal weight is at that level.

(B) The metabolisms of people who are usually not overweight are much more able to vary than the metabolisms of people who have been very overweight.

(C) The amount of calories that a person usually burns in a day is determined more by the amount that is consumed that day than by the current weight of the individual.

(D) Researchers have not yet determined whether the metabolic rates of formerly very overweight individuals can be accelerated by means of chemical agents. A

(E) Because of the constancy of their metabolic rates, people who are at their usual weight normally have as much difficulty gaining weight as they do losing it.

昨天看到一位nn的cr分类,把本题归于必要条件的逆否命题,我看了许久课还是觉得是排除他因(not+weaken),感觉og的解释也是说如果取非A,就会使结论错误,请nn帮我看看.