题目内容
No one knows when the first calendar was developed. But it seems possible that it was based on lunar months. When people started fanning, the sages of the tribes became very important. They studied the sky and gathered enough information to be able to predict when the seasons would change, and were able to announce when it was time to plant crops.
The divisions of time we use today were developed in ancient Babylonia 4,000 years ago. Babylonian astronomers believed the sun moved around the Earth every 365 days. They divided the trip into 12 equal parts, each with 30 days. Then they divided each day into 24 equal parts or hours, and divided each hour into 60 minutes, each minute into 60 seconds.
Humans have used many devices to measure time. he sundial was one of the earliest and simplest. However, the sundial worked well 0nly when the weather was fine, so other ways of measuring the passing of time were invented. One device was the hourglass. By the eighteenth century, people had developed mechanical clocks and watches. So we have devices to mark the passing of time, but what time is it now？ Clocks in different parts of the world do not show the same time at the same time, because time on Earth is set by the sun's position in the sky above us. As international communications and travel grew, it became clear that a way to establish a common time for 'all parts of the world was needed. In 1884, an international conference divided the world into 24 time zones, each zone represents 0ne hour. The astronomical observatory in Greenwich, England, was chosen as the starting point for the time zones. Twelve zones are west of Greenwich. Twelve arc east. The time at Greenwich measured by the sun is considered by astronomers to be Universal Time, also known as Greenwich Mean Time.
What does the passage mainly discuss？
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听力原文： Many American women believe breast cancer is the biggest threat to their health. But more than ten times as many women die of diseases of the heart and blood vessels. (30) The American Heart Association has new guidelines to help prevent heart attacks. For example, the guidelines urge women not to use hormone replacement therapy as a way to protect the heart. The guidelines also urge women to know their risk of heart attack or heart disease. They suggest that a woman talk to her doctor about this beginning as young as the age of twenty.
(31) The heart association Web site has information that can help people measure their level of risk. Users answer some questions. They enter their age and whether or not they smoke etc. A total score below ten percent is considered low risk. This means that a woman has less than a ten percent chance of a heart attack in the next ten years. The next level of ten to twenty percent is considered intermediate risk. More than twenty percent is high risk. (32) The heart association says those at high risk should ask their doctor for medicine. Women are also urged to ask for treatment if their blood pressure is one-hundred-forty over ninety or higher. The guidelines say women at intermediate or high risk should consider taking an aspirin each day. Aspirin may reduce the risk of a heart attack.
(31)
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