运用数据进行分析是历史学习的一种重要方法。图4反映出二战后在世界工业生产中西欧、日本所占比重不断提升的变化趋势。该“变化趋势”出现的原因是（   ）

①充分利用美国的援助②采用最先进的科学技术成果③资本主义国家发展不平衡的加剧④制定恰当的经济发展政策。

设变量x，y满足约束条件$\left\{\begin{array}{c}y\le x\\ x+y\ge 2\\ y\ge 3x-6\end{array}\right.$，则目标函数z=${\left(\frac{1}{2}\right)}^{2x+y}$的最大值为____ 

    Robots seem very new to most people. But they have a 1 history. A Greek scientist made the first robot. You may 2 robots in some movies. The robots in the movies are usually stronger, faster and 3 than people. In real life, most robots are used in factories. They can do lots of dangerous, difficult or4 jobs. Some people can't look 5 themselves and robots can help them. For example, some people can't see, and they use a guide dog to help themselves move. But now scientists are making a 6 to help them.

    Robots are also used in American hospitals. At one hospital, a robot 7 meals from the kitchen to the sick people's rooms. It never loses its 8 because it has a map of the hospital in its computer system(系统). 9 the future, robots will even work in space. But robots will 10 take the place of(代替)people but only work for people. They can, however, help us in a lot of different ways.