Rose's mother wants to take Rose to the zoo today. Many kinds of animals are in the zoo. So Rose is very happy.

    Rose and her mother go to see the tigers and lions first. Tigers and lions are scary so they lives in strong cages in the zoo. And they eat much meat every day.

    Rose sees two big elephants and a baby one. The elephants are very kind to people. Rose rides on an elephant and she is glad.

    Some cute pandas are in the zoo, too. They are a little shy. So people need to be very quiet when they go near them. Look! Five giraffes are there. They have long necks. They are from Africa(非洲). They like eating grass and leaves very much.

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圆(x-1)²+y²=1的圆心到直线$y=\frac{\sqrt{3}}{3}x$的距离是   （    ）

以下是我们生活中可见到的几种现象：①用力揉面团，面团形状发生变化；②篮球撞在篮球板上被弹回；③用力握小皮球，球变瘪；④一阵风把地面上的灰尘吹得漫天飞舞．在这些现象中，物体因为受力而改变运动状态的是 (    )

我们曾体验过以下一些声现象，其中能说明声音产生原因的是（    ）