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问题 选择题

含磷洗涤剂的使用是造成水体污染的主要原因之一．通常含磷洗涤剂中含有三聚磷酸钠，三聚磷酸钠的化学式为Na5P3O10，其中磷元素的化合价为（　　）

A．+3

B．+4

C．+5

D．+6

答案

根据在化合物中正负化合价代数和为零，Na5P3O10中磷元素的化合价为：（+1）×5+x×3+（-2）×10=0，

解得 x=+5，故选C．

单项选择题

在西方，________被誉为行政学的鼻祖。( )

A．威尔逊

B．梅奥

C．麦克雷戈

D．马斯洛
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单项选择题

In fall 2006, the National Basketball Association (NBA) started using basketballs made with synthetic, or man-made, material instead of leather. They made the change because they wanted every basketball they use to feel and bounce the same. Not all leather balls are exactly alike in weight or how they bounce, but the synthetic balls are.
However, some players complained right away that the new balls bounced differently and were actually harder to control than the leather ones.
Physics helped answer questions about why the new balls felt different. For example, the scientists studied friction, which in this case affects the ability of a player to hold onto a ball. "The greater the friction, the better it will stick to his hand," explains a scientist.
Tests on both wet and dry balls showed that while the synthetic ball was easier to hold onto when dry, it had less friction and became much harder to hold onto when wet. That’s because sweat stays on the surface of the synthetic balls but gets taken into the leather balls.
The scientists also tested bounce and found that the logo printed on the new balls made their surface uneven and caused them to bounce a little strangely compared with the leather balls.
In January, the NBA went back to using the leather balls. They aren’t perfect, but for now, that’s just the way the ball bounces.

The underlined word "They" in the last paragraph refers to ______.

A．the synthetic balls

B．the leather balls

C．the ball players

D．the scientists
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