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 .