听力题 According to some studies, the period from 6 a. m. to 10 a. m. is the average peak time for many major causes of death such as cancer and heart disease. Until recently doctors were taught that the human body lives in a stable state, changing little during the day. The science of chrono-biology — the study of how time affects life — is sparking a medical revolution by revealing how much our bodies change through daily rhythms. The natural biological rhythms are as vital as our heartbeats. By learning their secrets, we are discovering new ways to prevent and cure illness. There isn’t a function in your body that doesn’t have its own rhythm. The absence of rhythm is death. In other words, our interior biological clock stops working. Most people enjoy a peak in short-term memory and mental quickness in the late-morning hours until shortly before noon. Then a measurable dip in energy and efficiency begins around 1 p. m. In the afternoon, exercise endurance, reaction time and manual ability are at their highest. Our daily rhythms can bring a dark side to the early evening, however. These hours include a second daily peak in heart attacks, although smaller than the morning’s. Around 7 p.m., alcohol takes longer to be cleared by your liver. By understanding our body clocks, we can improve our health and continue to foster our survival. Without grasping, for instance, that our natural temperature rises one to two degrees from morning until evening, we could misjudge thermometer readings. A temperature of 99 degrees might signal perfect health at 5 p.m. but illness at 7 a.m.