Thousands of years ago，human(人类)didn’t live in towns．Sometimes they would live in caves(洞穴)or build camps in the forest．
Only about thirty people1 in each camp．The men would go hunting while the woman and children2food from trees around the camp．All the food was 3 among people in the group．Every few weeks they moved to another place to find more food．It was a simple life，but people had to be 4 .They had to make everything that they needed，and they had to know a lot about plants and animals．
Nowadays most people live in towns and cities，and they work in offices and factories．Life is 5than in the old days．There are fewer 6，but there is less excitement．Some people go7  excitement  sailing round the world．climbing mountains，or exploring(探测)caves．
Most people look forward to the8,a time when they can enjoy a change from the normal life．For some this means going camping．But camping today is 9 from camping in the past．Gas cookers，ready-made food and air-beds mean people can camp much more10 than they did in the old times．

设全集U=R，集合$A=\left\{x|x\ge 2\right\},B=\left\{x|0\le x<5\right\}$则集合$\left(C_{U}A\right)\cap B$=（ ）

阅读短文，回答问题：

星系在远离我们而去

当一列火车迎面驶来时，我们听到的汽笛声音调会升高（即声波的频率升高）；当它离我们远去时，音调降低（即声波的频率降低），这一现象叫多普勒效应．

光同样可以产生多普勒效应，当一个光源靠近我们或离我们远去时，我们观测到它发出的光的频率也会发生变化，变化的规律也会发生变化，变化的规律与声音发生多普勒效应的规律相同．

20世纪天文学家哈勃观察到，几乎所有远处星系发出光的频率都向红光方向偏移，称为“红移”，这一现象说明，星系在远离我们而去，哈勃研究了24个距离已知的星系，由它们进行的速度v与它们离我们的距离r的图象，如图所示，并据此，得出它们退行的速度v与它们离我们的距离r的关系﹣“哈勃定律”．

为解释哈勃定律，科学家提出“宇宙大爆炸”理论，认为宇宙是从一个大爆炸的火球开始形成的，假设我们就位于其中心，大爆炸后各星系以不同的速度向外匀速运动，远离我们而去．

如图所示，竖直墙壁两侧固定着两轻质弹簧，水平面光滑，一弹性小球在两弹簧间往复运动，把小球和弹簧视为一个系统，则小球在运动过程中（   ）