求解，我们一同成长，挑战GMAT吧

yanxihua00 · 发表于 2011-3-8 10:39:16

If athletes want better performances, they should train at high altitudes. At higher altitudes, the body has more red blood cells per unit volume of blood than at sea level. The red blood cells transport oxygen, which will improve performance if available in greater amounts. The blood of an athlete who trains at high altitudes will transport more oxygen per unit volume of blood, improving the athlete's performance.

Which of the following, if true, would be most damaging to the argument above, provided that the athlete's heart rate is the same at high and low altitudes?
(A) Scientists have found that an athlete's heart requires a period of time to adjust to working at high altitudes.
(B) Scientists have found that the body's total volume of blood declines by as much as 25 percent at high altitudes.
(C) Middle-distance runners who train at high altitudes sometimes lose races to middle-distance runners who train at sea level.
(D)The performances of athletes in competitions at all altitudes have improved markedly during the past twenty years.
(E) At altitudes above 5,500 feet, middle-distance runners often better their sea-level running times by several seconds
这是一道削弱题，削弱的地方是运动员的心脏跳率在高海拔和低海拔都是一样的，可是题目中并没有说心脏速率，不过是说每寸的血液的体积。。。。。如果要削弱，不就是要建立它们之间的联系吗？可是答案就是没有，我实在看不懂，请教大家，谢谢。。。。

sdcar2010 · 发表于 2011-3-8 10:58:23

This a math question.

If B is true, then it is possible that the TOTAL amount of oxygen transferred at high altitudes is smaller than at sea level since the available volume of blood decreases at high altitudes.

Total O2 tranported = [concentration of red blood cell]*[total volume of blood]

yanxihua00 · 发表于 2011-3-8 11:28:02

谢谢，我明白了，是我把题目意思没搞清楚，可是还有一个问题，per unit volume of blood 和total volume of blood 。。。。前提是心律一样，是不是也就是说units 一样？所以，才可以推出这个结论。。如果假设在高海拔和低海拔的Units 是不一样的，怎么能比较出来呢？因为题目中是说在at higher altitude, the body has more red blood cells red blood cells per unit volume of blood than at sea level. 题目中是per, 而不是total, 或者说是不是我有点抠字眼了？谢谢哈

sdcar2010 · 发表于 2011-3-8 11:49:25

The heart beat thing is to make the playing field fair and level since with a faster pumping rate, more red cells can be tranported (together with the bound oxygen).

Per unit of blood has nothing to do with heart rate. It deals with the concentration of red cells in the same volume of blood, either at sea level or at high altitudes. Units will always be the same.

yanxihua00 · 发表于 2011-3-8 17:05:02

thanks u~~

求解，我们一同成长，挑战GMAT吧

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