题目内容：
第50题___________
A．Such persons have a weak or damaged heart, high blood pressure, or other problems of the blood system. B．Several of these conditions are present at the same time.
C．Most people suffer only muscle pain as a result of heat stress.
D．Several hot days are considered a heat wave.
E．So does extreme heat.
F．Doctors say people can do many things to protect themselves from the dangers of extreme heat.
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