使用显微镜时，被观察物体离物镜的距离     （   ）

丰富的地面生物资源是各种生物生存、繁衍的物质基础，也是人类衣食住行的主要来源．我们吃的粮食、蔬菜、水果以及肉、蛋、奶大多来自地面上的动植物．

阅读下面材料，在空白处填入适当的内容(1个单词)或括号内单词的正确形式。

      “Equal pay for equal work” is a phrase by the American women who feel they are ____ (fair) treated by society.They think it is not right for women to be paid less than men for the____ amount of work.Some people say men have ____  (many) duties than women.A married man has to earn money to support his family and make important ____ (decide)，so it is right for them to be paid more.Some are even against married women ____ (work) at all.When wives go out to work，they say，the home and children are given no attention ____ ．If women are encouraged by equal pay to take up jobs，they will be ____ (able) to do the things that they are best at doing：making a nice home and bringing ____ children.Women who disagree say that they want to escape from the limited place which society wishes them to fill and have ____ freedom to choose between a job and home life，____ a mixture of the two.In fact women have the right not only to equal pay but also to equal chances.