题目内容：
请在第__(49)__处填上正确答案。
A．Such persons have a weak or damaged heart, high blood pressure, or otherproblems 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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