试题与答案

测量值与真实值之差在测量值中所占的比例为( )。 A.绝对误差 B.相对误差 C.

题型:单项选择题

题目:

测量值与真实值之差在测量值中所占的比例为( )。

A.绝对误差
B.相对误差
C.系统误差
D.偶然误差

答案:

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参考答案:B解析:[要点解析] 由题干中关键信息“每个部门有若干名员工,每种商品只能由一个部门负责销售”可知,实体“部门”与“员工”是一对多(1:n)的联系,实体“部门”与“商品”也是一对多(1:n)的联系。表...

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Intense physical exercise is not the only way to better health. Studies show that walking several times a week can lower risk of many diseases. They include heart disease, stroke, diabetes, bone loss, arthritis (关节炎), and depression. Walking also can help you lose weight.
Fast walking is good for the heart. It lowers the blood pressure. It raises the amount of good cholesterol(胆固醇)in the blood. Researchers say walking can sharply reduce the risk of suffering a heart attack.
Studies have also shown that walking for 30 minutes a day can delay and possibly prevent the development of diabetes. People who are overweight have an especially high risk to develop this disease.
Walking strengthens the muscles and builds up the bones that they are attached to. Studies show that walking could decrease the risk of developing osteoporosis (骨质疏松症). Walking can also help ease the pain of arthritis in areas where bones are joined. This is because walking strengthens the muscles around the bones.
Experts say walking is one of the safest ways to exercise. There is a low risk of injuries. So it is good for people who are starting an exercise program for the first time and for older people.
A walking program is easy to start. You should wear loose clothes and good shoes. There are shoes that are designed especially for lots of walking.
How fast should you walk? For the best effect, doctors say you should walk fast enough to cause you to breathe hard. Yet you should still be able to talk. Let your arms move freely while you walk.
There are no rules to starting a walking program. You might walk short distances. Or you might walk up hills to strengthen your leg muscles. Health experts say you can gain the most from a walking program if you walk at about five kilogmeters an hour for 30 minutes a day. You should do this about five times a week.
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                     (小题3:)___________the blood pressure
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