A、Heart disease. B、Severe headache. C、Heat stress. D、Muscle pain. C

Extremely hot weather is common in many parts of the world. Although hot weather just makes most people feel hot, it can cause serious medical problems—even death. Experts say heat may be nature’s deadliest killer.
    Several hot days that follow each other are considered a heat wave. (26) Experts say heat waves often become dangerous when the nighttime temperature does not drop much from the highest daytime temperature. This causes great stress on the human body.
    Doctors say people can do many things to protect themselves from the dangers of extreme heat. Stay out of the sun, if possible. Drink lots of cool water. Wear light colored clothing made of natural materials. Make sure the clothing is loose, permitting freedom of movement. Also, learn the danger signs of the medical problems linked to heat.
    The most common health problem linked to hot weather is heat stress. Usually, it is also the least severe. The causes of heat stress include wearing heavy clothing, physical work or exercise, hot weather and high humidity. If several of these conditions are present at the same time, a person’s body temperature may rise above safe levels.
    Most people suffer only muscle pain because of heat stress. The pain is a warning that the body is becoming too hot. Doctors say those suffering muscle pain should stop all activity and rest in a cool place. (28) Doctors say not to return to physical activity for a few hours because serious conditions could develop.
26. When will heat waves become dangerous according to experts?
27. What is the most common health problem related to hot weather?
28. Why can’t one return to physical activity immediately when suffering from muscle pain?