问题
单项选择题
某种瓶装药水的样本标准差s=8g，若瓶子的质量均为2g，则药水的样本标准差为______。
A．4.0g
B．1.7g
C．8g
D．9.7g
答案
参考答案：C
解析：同上题，减去瓶子重量后的药水的样本标准差不变。
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某种瓶装药水的样本标准差s=8g，若瓶子的质量均为2g，则药水的样本标准差为______。
A．4.0g
B．1.7g
C．8g
D．9.7g
参考答案：C
解析：同上题，减去瓶子重量后的药水的样本标准差不变。
Now more and more people get to know that exercise is important. We need to exercise. Doctors say it is good for us. It makes us and healthier. who often exercise are more alert (机灵的). This means they do in exams and schoolwork than those who don’t exercise. There are many ways . You can walk, run, swim, or play ball games. You have to like you’re doing. Try all kinds of things you find one, two, or even three sports that you feel right for you. It’s best to exercise twice a week. Thirty minutes each time enough (足够的). You can exercise at fitness centres (健身中心). They have a lot of equipment (器材). The equipment can exercise your arms, legs and other parts of your body you healthy. Some people buy equipment for their homes, but it is very expensive.
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