定滑轮实质上是一个 杠杆，动滑轮实质上是动力臂是阻力臂 的杠杆，所以使用它可以

     Life in 30 years will be   1_  because many changes will take place,but what will the changes be?      
     The population is growing fast. There will be    2   people in the world and most of them will live longer than before. Computers will be    3   smaller and more useful,and there will be at least one in every home. And computer studies will be one of the important   4   inschool.    
     People will work fewer hours than they are doing now,and they will have more free time for sports,
watching TV and traveling. Traveling will be much cheaper and  5_  . And many more people will go to
other countries   6_  holidays.    
     There will be changes in our food,too. More land will be used for    7   new towns and houses. Then
there will be less   8_  for cows and sheep,so meat will be more expensive. Maybe people won't eat it
every day.They will eat more vegetables and fruit instead. Maybe people will be healthier.    
     Work in the future will be different,too. Dangerous and hard work will   9_  by robots. Because of
this, many people will not have   10   to do. This will be a problem.