完形填空,阅读下面的短文，从短文后各题所给的选项中选出能填入空白处的最佳答案。

Bees live in a house that is called a hive. There are three kinds of bees: workers, drones (雄蜂) 1queens. Only one queen bee can live in each hive. If she is lost or dead, the other bees 2 their work.

Workers are very clever and busy. They all join together3 small rooms called cells of wax for their honey. Each worker bee does its own work. Some go out and collect honey from the flowers; 4 stay at home and work inside the hive. The cells5have six sides are made by worker bees. Did you ever look into a glass hive and see them while at work? It is 6to see how busy they always are. Before winter comes, all the drones are driven from the hive7 they don't eat the honey they did not collect.

It is not safe 8 children to be too close to bees. Bees have painful stings they use in their defense (防御).

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    We know the earth is a planet．There are seven other planets，and they go  1 the sun together．The eight planets and the sun are2 the solar system．The first planet，3   the sun，is Mercury(水星)．It is 58 miIlion  4  from the sun．Venus(金星)is the second planetfrom the sun，and  5 planet，the earth，is the third．It is from the sun,and 55  planet,the earth,is the third.It is 2,650 million kilometres from the sun．

    Jupiter(木星)，Saturn(土星)，Neptune(海王星)and Uranus(天王星)are all 6 than the earth，7 Venus，Mars and Mercury are smaller than the earth．

    Animals，trees and humans can only 8  on the earth，because the other planets in our solar system don't  9  air or water．Do any  10planets in   solar systems have life?We don't know about it．

    I can't remember when I started collecting litter. But it was when I got tired of 1 litter nearby that I realized no one else was going to pick it up.

    I live near a forest in Ohio, America. I can walk there  2 three minutes. I used to love going there to play with my dog. But one day there was 3 much litter there that I became very unhappy. I decided to clean up the forest, and I wanted to 4 happy when I went again. I made my first trip to clean the forest that afternoon. I took a big black rubbish bag with me. Ten minutes 5  I started to pick up litter, my bag was full! There were cans, bottles, broken glass and newspapers in it.

    From then on, I 6  to the forest four times a year to pick up litter. I often stay there for three hours. It makes me feel 7 to do something for the environment. After each trip, I look through all the litter that I've collected. If 8  of it is recyclable（可回收利用的）, I'll keep it. I can't understand why people drop litter. But I will keep on picking it up  9they stop dropping it. I know I am only doing a small bit  10 the earth, but I still think it is important.

    Many people say that they have seen flying saucers（飞碟） in the sky. 1 can these things be?

    Some people think that they are spaceships from other planets. Doctors 2 that perhaps they are only a weakness of the eyes. It is possible that they are our own planes 3 very high. Or are they birds with the sun's light on them?

    But some people say that they have seen them 4. They have seen beings（人） get off them and walk around. They have 5 to those beings, sometimes in English. People have 6 photos of flying saucers and of these beings. We have seen the photos, but sometimes the people had to take them in a 7. Children have seen flying saucers, and even dogs have seen them. Perhaps we do not think that the 8 of children, or dogs are important. But school-teachers have 9 seen them and Air Force officers and 10 policemen. Must we not listen to these people?

    Have you heard of STEM education? STEM 1 Science, Technology, Engineering and Mathematics. It means students can learn these 2subjects in one class. And they work on many projects to practice 3 they learn STEM education is very 4 in the US.

    Now more than 600 5 middle schools bring in STEM education, according to the paper, en. Beijing, Yuying School is one of them.

    The school 6 the course in May. It invited college teachers to teach more than 80 students programming, robotics and other interdisciplinary(跨学科}的) knowledge.

    The teaching style is quite 7, Once teachers finish teaching basie knowledge, studentes will practice it 8. For example, after learning about electrie circuits(电路),students are required to design one that could control three lights 9.They have many projects to improve their hands-on 10 as well. Once, they had a "smart home" model design project. All the students competed to design a 11 model and make it "smart" .Liu Tianyou, 12, with 12 teammates, used computer programs and sensors to finish it. "If you open the door of the house, the lights will 13 automatically, "he said. Their work won the third prize.

    The class, develops students' creativity as well. 14 Learning mechanies and programming in the class, Zhao Hngyi, 14, made a Lego robot himself in eight 15.From assembling(组装)to testing he finished it on his own. The robot can catch things and walk on certain tracks under orders. " It's cool to make my idea come to life," he said.

    Today more and more people live in cities. So there is usually little room in a city to grow food.1of the land in a city is used 2 homes, shops, roads and parks. Most food for city people is grown in the country. It is often brought to the city by3, train and plane. Some food 4 comes into the city by car.

    Water is5 thing that cities get from the country. Everyone needs water every day. We use a little of it for6, but we use even more to 7bathtubs(浴缸) and wash streets.

    The water used in cities comes mostly from the rain. But people8use the rain that falls on cities. The rain becomes dirty as it falls through dirty air. Once it hits city buildings or streets, the rain will pick up more dirt. It is not good for drinking or bathing.

So cities must reach out to the 9 country for water. There the rain falls through air onto trees and grass. The fallen rain runs 10 rivers and lakes. So it is important to keep both cities and the country clean.