Air is all round us．It is around us___31____we walk and play．From the time we are born，air is around us on every side．When we sit down，it is around us．When we go to bed．air is  32 around us．We live  33 air．
All living things  34 air．Living things cannot live  35  air．We can live without any water for  36 days，but we cannot live for more   37 a few minutes without air．When we are working  38 running，we need more air．When we are asleep，we need less air
We live in air but we cannot see it．We can only feel it．We can feel it when it is  39 ．  Moving air  40 wind．  

Electric bicycles which run on battery-operated (电瓶) motors are winning over riders of ordinary bikes   41 their speed, quality and environmental advantage.
They were first   42 on 1980s in China, but the selling was not very good. Today, thanks 43  improvements on battery quality, the electric bikes sell well. There are now more than 100 electric bicycle producers in China and 26 million such bicycles were produced in 2011. Japan is another large  44  of such bicycles in the world with a total production reaching 381,721in 2010.
  45 China is one of the largest producers of electric bicycles in the world, the   46  of its producers with mass production (大批量生产) is actually small.
Electric bicycles are still   47 in China. Time is needed for people to become familiar with them and accept them. Each bike’s price of between 2,000 yuan (US $318) and 3,000 yuan (US $477) is still  48  for ordinary citizens (民众). Although such bikes are quick, safe and 49 to operate, their batteries still have shortcomings (不足). They weigh more than 10 kilograms; their service life is   50  two years and they   51  400 yuan each.
There were more than 450 million bikes in China in 2006. If just one percent of all these bikes are replaced by electric  52  , the market will be very large. And   53  the battery is further improved and the price is    54   , many of us will not be able to keep back from    55  the latest electric bikes

How many plastic bags do you use every day? 46 there any chance for us to live without them? What can we do to have 47   plastic pollution? A performance in Hangzhou makes people   48  more about the overuse of plastic bags in our lives.
In front of a supermarket in Hangzhou , five volunteers 49  white plastic bags and walked around and through the crowd. The performance   50  people to use more cloth bags  51     plastic ones.
Some of the plastic bags worn by the performers were collected from customers in two food markets and 52  were collected by 700 students from a middle school.
On that day, when leaving the food markets, customers were told to hand over 53  plastic shopping bags. 54  plastic bags were collected in two hours.
“ If we do 55  about it, the earth will be eaten up by white pollution. And 56  will become ‘plastic men’,”said one of the performers.
“How can you breathe in 57  plastic bags?” A   58   woman asked one performer.“How can the earth breathe 59   there are too many plastic bags?”the performer answered.
Starting in June 2008,plastic bags were 60  given for free in supermarkets,shopping malls or food markets all over the country.
People are called on﹙号召﹚to use cloth bags when they go shopping.

How did I become known as a "rubbish picker '?  
I never   36   rubbish before.  I didn't care where it went or who cleaned it up.  But two years ago, I started caring about it deeply.  I lived near a forest in Ohio, America.  I can walk there    37   three minutes! I used to love going there to play with my dog.  One day there was   38   much rubbish there that I became very unhappy.  I decided to clean up the forest.  I want to   39   happy going there again. I made my first trip to clean the forest that afternoon.  I took a big black rubbish bag with me. Ten minutes    40   I started to pick up rubbish, my bag was full! From then on, I go to the forest four times a year   41   rubbish, it makes me feel   42  to do something for the environment. After each trip, I look at all the rubbish that I've found.  If   43   of it is recyclable, I keep it.  I will keep picking up 44---people stop dropping it.  I know I am only doing a small bit 45   the earth, but I think it is important.

Is your schoolbag too heavy? The e-schoolbag will help you. It is said that e-schoolbags are going to be brought into   43  in Chinese middle schools soon.
Heavy schoolbags have been a serious   44  for a long time. But the e-schoolbag will  45 . An e-schoolbag is  46  lighter than a usual schoolbag. Perhaps, the e-schoolbag should be   47  an e-textbook. It is a small computer for students. It is as   48  as a usual book,   49  it can still have all the things for study, such as textbooks, exercise books and so on which can be made   50  chips(芯片) like stamps. The students can read the text page by page on the screen, take notes, or even send e-mails to their teachers. They only need to   51  the right chip into the e-schoolbag. Then they can use it.
Some people say   52  e-textbooks can be easily broken, while others say it is not good for eyes. But only time will tell.

IQ（intelligence quotient智商）is a score that shows a person’s level of intelligence.
People used to believe that some people are born with a high IQ and some aren’t.
  32 , a study by scientist at University College London has challenged（挑战）this idea. According to an article last October on the Journal Nature, scientists are beginning to think that our IQ is not a constant（不变的）score.
The scientists tested 33 healthy young people in 2004 between the ages of 12 and 16. Then they did tests again four years later, when the same people were between 16 and 20.
Scientists found big changes in the IQ scores between 2008 and 2004. Some  33 and some fell  34 as many as 21 points.
To test whether these scores were meaningful, the scientists compared them with results from brain scans（扫描）. They found that the IQ changes matched changes in the structure（结构）of the subjects’ brains. “A change in 20 points is a huge  35 ,” said Professor Cathy Price, who led the research. He said it could mean the difference between an average and a  36 person. The team has not found a clear cause for these changes. However, they say it is  37 that education plays a role in changing IQ.
“Here we have shown that children’s  38 is likely to be still developing, ” says Price. “We have to be careful not to write off  39 performers at an early stage. In fact, their IQ may improve in a few more years. ”

Electronic books have changed the way many people read for   15 . Now online textbooks are changing the way some students learn and some teachers teach.
More than   16  students go to the public schools in Fairfax County, Virginia, outside Washington. Last year, the school system used digital books in fifteen schools. This school year, middle schools and high schools changed   17  printed to electronic textbooks in their social studies classes.
“I mean, it’s just   18  a regular textbook, except it’s got it all online.” says Luke Rosa, a history teacher at Falls Church High School.
Peter Noonan, an assistant superintendent(主管) of schools says, “The world’s changing   19 . And the online textbooks can change right along with the events that   20 .”
“Digital books also cost   21  than printed textbooks,” he says, “Usually it’s between fifty and seventy dollars   22  a textbook for each student, which adds up to about eight million dollars for all of our students in Fairfax County. In fact, we have bought all of the online textbooks for our students for just under six million dollars.”
Social studies teacher Michael Bambara says the e-book he uses in his government class is better than a(an)   23  textbook. It has materials for students   24  different levels of reading skills…

Many people like to  36   the Internet. Exploring the Internet is one of the most important activities of the day. The Internet brings the outside world closer to people’s   37  . Some people say the world is smaller than before    38   of the Internet.　　
What’s  39   in other countries?  40  do people live in places far away? Is there an 41   sports game somewhere?   42  life like in the deepest part of sea? If you want to answer all these questions, just come to the Internet.    43   people can also learn through reading or listening to the radio. But with the Internet they can learn better and  44 . A lot of information can  45  at a great speed.
Can we go shopping without leaving home? Can we see a doctor without going to the school? Can we see a 46  without going to the hospital? —All these things seemed impossible but now they have become quite 47  .
The Internet helps us open our eyes. It also helps us 48   our minds. The Internet often gives us new ideas.   49   , it helps us in many ways. Great changes have taken place  50  the use of the Internet.

Trees are one of the oldest plants on the earth. Just like us, trees change a lot  1 they grow. At one to three years old, young trees learn to   2  themselves. For example, many tree grow thorns (刺)to tell animals  3 near. Most young trees have large and deep green leaves to  4  enough sunlight and turn it into their food and energy. When trees are four years old, they are strong enough to  5 the challenge(挑战)in life. At the age of fifteen, they become young adults and grow more   6 . They will have their own flowers and fruit. After the trees are twenty to twenty-five years old, they are called real adults because they reach their  7 . Adults trees give us oxygen and natural beauty. If we  8 them very well, they will live healthily for many years. As time goes on, trees begin older and older and even  9 . At this time, they still have their important places in nature and uses for people.  10 many ways, the life of trees is like our own life experience.

I’d like to tell you about my dream classroom in the future．My classroom will be very  31  ，so we can do lots of activities in the classroom．In summer，it will be  32  and in winter it will be warm，so it will be  33  ．There will be a beautiful garden in front of it．We can see many trees and  34 in it．There will be a cable TV in our classroom and we can  35  it at noon．Everyone will have a  36  on the desk，so we can read information  37  the Internet．The lessons will be interesting．We  38  use pens or pencils．We will use computers to do our homework．The teachers won’t use  39  to write on the blackboard．They will  40  the lessons with the help of the computer．