LSAT-3-1-15.help feifei-92

LSAT-3-I-15.
Baking for winter holidays is tradition that may have a sound medical basis. In midwinter, when days are short, many people suffer from a specific type of seasonal depression caused by lack of sunlight. Carbohydrates, both sugars and starches, boost the brain's levels of serotonin, a neurotransmitter that improve the mood. In this respect, carbon hydrates act on the brain in the same way as some antidepressants, Thus, eating holiday cookies may provide an effective form of self-prescribed medication.

Which one of the following can be properly inferred from the passage?

(A) Seasonal depression is one of the most easily treated forms of depression.
(B) Lack of sunlight lowers the level of serotonin in the brain.
(C) People are more likely to be depressed in midwinter than at other times of the year.
(D) Some antidepressants act by changing the brain's level of serotonin.
(E) Raising the level of neurotransmitters in the brain effectively relieves depression.

The key is D, but what’s wrong with B ?

My reseasoning is as flwg;

1,lack of sunlight(A) ==>depression(B)

2,boost levels of serotonin(C)==>improves the mood(negative B) , so B==>negative C

1+2: A==>B==>negative C,thus lack of sunlight lower the levels of serotonin

What is wrong in the reasoning? Offer your help pls.

In my opinion, improves the mood will not necessarily be negative

B(depression)

1。原文并没有充分必要关系，所以不存在逆否命题的问题。所以你的推理从一开始就是错的。没有出现象IF， UNLESS，ONLY等等词，就不要搞什麽逆否命题。

2。提高levels of serotonin会提高情绪，但情绪低落不一定levels of serotonin降低，因为有可能多种原因影响情绪

还是有点不明白，是不是说这是因果关系所以不成立阿，否则的话

提高levels of serotonin会提高情绪a->b,情绪低落->levels of serotonin降低不就是b否->a否,那么不就成了逆否命题，不久成立了么

如果是因果关系的话，能不能说一下怎么辨别因果关系还是充分关系啊？谢谢