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The police can do many things for people. They help to keep our things and us safe(安全的). They help cars and buses move safely. The police go around our cities to see that everything is all right.
and they can help them find their parents. If you don’t know the way to a place, you can ask the police.
Some police stand at crossings(十字路口). They don’t let the cars go too fast. They help children and old people cross the street.
The police help us in many ways. We need them. We should thank them for a job well done.
| A．Sometimes they find lost children |
| B．They do a good job. |
| C．They tell the cars when to go and when to stop. |
| D．They know all the streets and roads well. |
E. They take people to a hospital when they are hurt (受伤) .
Do you have a tail？ Of course not， we know． But tails are like opinions． actually， everyone has them： fishes， birds， most reptiles， and even some of our closest relatives．
Since tails first evolved（进化） at least 500 million years ago． Geckos （壁虎）use them to store fat， birds use them to steer through the air． But for most mammals （哺乳动物），（1） Yet， as you get closer to humans on the evolutionary tree， tails disappear， Gorillas（大猩猩）don' t have them， and neither do chimps（黑猩猩） or any other apes （类人猿）， including us， of course． To understand why， take a look at how we walk．
（2） walking like this gives us a huge advantage because unlike four﹣legged animals，which have to pour energy into every step they take， two legs take advantage of gravity（重力），which does some of the work for us． You see， each time we take a step， gravity pulls us forward．The end result is that when we walk， we use around 25% less energy than walking on all fours， and this way of getting around also totally eliminates（淘汰） the need for a tail．
It's said that you can still see a reminder of a time when our ancient ancestors had one． Just look at a human spine（脊椎）．（3） That's your tailbone． It's all that's the rest of our tail．
Now， babies are born with what looks like a tail， but that's not what's really going on． Most often， these tails are actually a parasitic twin（寄生物）． These types of tails usually form as a birth defect（瑕疵）．（4）
So the tail of humans has gone， it's the result of evolution millions of years Will humans be much taller， stronger or smarter in the future？
| A． Nowadays， humans can walk completely upright． B． And in these situations， doctors will advise to remove the tails with no harm to the babies． C． they serve one major purpose﹣﹣balance． D． You can see how the last few bones are partly fused（融合） together． |
为了实现中国梦，我们必须努力学习和工作．
to achieve our Chinese Dream， we must study and work hard．
在科学家们的努力下，中国已经能够制造像 C919 这样的大飞机．
With scientists' great efforts， China has to make big planes like C919．
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