阅读理解
If you're training for a marathon , a proper plan for water intake (摄入) is important . Of course , there's
the risk of dehydration (脱水) . But athletes now know they can also get into trouble by drinking to much .
To much water intake can lower levels of sodium (钠) in the blood . The death of a 28-year-old woman
following the Boston Marathon caught the attention of many runners and led to new research .
Experts advise long distance runners to replace the liquids they sweat out . Their goal is to try to keep
someone from not getting dehydrated by more than 2 percent of their body weight .
One technique for deciding how much water you need is to get the exact numbers . Runners have to
weight themselves before and after a run to determine how much water they've lost . If their weight drops
by more than 2 percent , they have not drunk enough water.
Hyponatremia occurs when runners drink so much water that blood salt levels drop off . A study
published last year tested 488 runners who completed the Boston Marathon and found 13 percent of them
had dangerously low blood salt levels . The first sign that runners may notice is slightly swelling in the
hands . They can't get their rings off , and then they might feel sick . They may not remember where they
are . In fact , most runners get enough salt to get back to normal levels by eating just one meal after a run .
Contrary to the old advice that runners should drink as much as they can to prevent dehydration , the new
research has shown that the body is a remarkable machine that actually tells you via thirst when you need
water .
1．The author of this passage is primarily concerned with        .
A．the signs and treatment for dehydration
B．the long distance runners who need help
C．how to manage water intake during a marathon
D．a 28-year-old woman who died after a Boston Marathon
2．Why do runners have to weigh themselves before and after a run ?
A．They can improve their performance in a run .
B．They can learn how much salt there is in the blood .
C．They ca know the quantity of water they've lost during a run .
D．They can decide what kind of water they should take during a run .
3．What conclusion can we draw from the passage ?
A．Taking much salt during a run can avoid selling in the body .
B．Either too much or to little of water intake is harmful .
C．A rich meal is helpful to our performance in a run .
D．We should take enough salt during a run .
4．According the passage, which of the following statements is correct ?
A．Too much water intake→blood sodium levels ?→dehydration .
B．Too much water intake→blood salt levels ?→hyponatremia .
C．No water intake→blood sodium levels↑→hyponatremia .
D．No water intake →blood salt levels ?→hyponatrenmia .

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