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问题 单项选择题

愚人节：4月1日

A．世界无烟扫：3月15日

B．世界艾滋病日：3月12日

C．世界环境日：3月1日

D．中国植树节：3月12日

答案

参考答案：D

解析： 愚人节是4月1日，中国植树节是3月12日。

选择题

下列关于排泄的叙述中，哪一项是不正确的[ ]

A．肺呼出二氧化碳属于排泄

B．肛门排出粪便属于排泄

C．皮肤的汗腺分泌汗液属于排泄

D．尿液的排出属于排泄
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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 synthetic ball bounces differently from the leather one mainly because ______.

A．it is wet

B．it is dry

C．there’s a logo on it

D．its weight remains the same
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