Life in the year 2050 will be 1 from today. Between then and now many changes will take place. But what 2 the changes be?

    The population(人口)is growing fast. There will be 3 people in the world and most of them will live 4 than people live now.

    Computers will be much 5 and more useful, and there will be at least one in every home. And computer studies will be one of the most important subjects in 6 then.

    People will work 7 hours than they do now and they will have more free time for sports, 8 TV and traveling.9will be 10 cheaper and easier. And more people will go to other countries on 11.

    12 will be changes in our food, too. More land will 13 for building new towns and houses. Then there will be less land for keeping cows and sheep, so meat will be more expensive. Maybe no one will eat it every day. Instead they will eat more fruit and vegetables. Maybe people will be healthier.

    Work in the future will be different, too. Dangerous and hard work will be done 14 robots. Because of this, many people will not have enough work to do. This will be a 15.

阅读理解

    Mark Twain, the famous American writer and a great master of humor, liked to play jokes on others. But once a joke was played on him. One day Mark Twain was invited to give a talk in a small town. At lunch he met a young man, one of his friends.

    The young man said that he had an uncle with him. He told Mark Twain that his uncle never laughed or smiled, and that nobody and nothing was able to make his uncle smile or laugh.

    "You bring your uncle to my talk this evening," said Mark Twain. "I'm sure I can make him laugh."

    That evening the young man and his uncle sat in the front. Mark Twain began to speak. He told several funny stories and made everyone in the room laugh. But the man never even smiled. Mark Twain told more funny stories, but the old man still kept quiet. Mark Twain continued to tell his funny stories. Finally he stopped. He was tired and quite disappointed.

    Some days later, Mark Twain told another friend what had happened." Oh," said his friend, "I know that man. He's been deaf for years."

某同学利用天平和量筒测量小石块的密度，下列操作步骤中不必要的是（　　）