[求助]OG-10-20中两个错误选项的条件推理关系

Increases in the level of high-density lipoprotein (HDL) in the human bloodstream lower bloodstream-cholesterol levels by increasing the body’s capacity to rid itself of excess cholesterol. Levels of HDL in the bloodstream of some individuals are significantly increased by a program of regular exercise and weight reduction.

Which of the following can be correctly inferred from the statements above?

(A) Individuals who are underweight do not run any risk of developing high levels of cholesterol in the bloodstream.

(B) Individuals who do not exercise regularly have a high risk of developing high levels of cholesterol in the bloodstream late in life.

(C) Exercise and weight reduction are the most effective methods of lowering bloodstream cholesterol levels in humans.

(D) A program of regular exercise and weight reduction lowers cholesterol levels in the bloodstream of some individuals.（D）

(E) Only regular exercise is necessary to decrease cholesterol levels in the bloodstream of individuals of average weight.

根据OG上的解释，B和E中的不能锻炼构成增加HDL或者减少胆固醇的必要或者充分条件。

我搞不清楚到底选项B或者E中，哪个锻炼是必要条件、哪个是充分条件？

根据题目意思

regular exercise and weight reduction－－－>HDL significantly increased －－－>lower  bloodstream-cholesterol levels （通过自身清除能力的增加）

选D

B说：No 【regular exercise and weight reduction】－－－>胆固醇水平高。根据题目推理链这是推不出来的。题目只告诉我们如何来降低。没有说什么会增高。

E说：只有锻炼对于体重一般的人是必要的来降低胆固醇的水平。题目没有说【锻炼和降低体重】是仅有的两个方法，因此不能说，因为体重已经是平均水平，因此仅有进行锻炼才能降低胆固醇的水平。和B一样，还是推不出来的