卫星地球站天线系统的主要作用是（）

[问答题]Practice 9　　In the United States most people are simultaneously consumers and producers; they are also voters who help influence the decisions of the government. The mixture among consumers, producers and government changes constantly, making a dynamic rather than a static economy. In the last decade consumers have made their concern known and government has responded by creating agencies to protect consumer interests and promote the general public welfare. In another development, the population and the labor force have moved dramatically from farms to cities, from the fields to the factories, and above all to service industries, thus providing more personal and public services. In today's economy these providers of services far outnumber producers of agricultural and manufactured goods.　　Generally, there are three kinds of businesses: (1) those started and managed personally by single owners or single entrepreneurs; (2) the partnership where two or more people share the risks and rewards of a business, and (3) the corporation where shareholders as owners can buy and sell their shares at any time on the open market. This latter structure, by far the most important, permits the amassing of large sums of money by combining investment of many people, making possible large-scale enterprises.

[判断题]从认识论的角度看，教学是教师教学生认识世界的活动。

[单选题]《汉书》是我国第一部断代史，它的编纂体例是（　　）。

[问答题]简述19世纪现实主义的主要特征。

[判断题]推铅球时，铅球应完全落在落地区标志线外沿以内。

[问答题]如何认定使用与知名商品近似的名称、包装、装潢的行为？

[单选题]以下哪个土壤中的金属离子毒害性较小，对人体健康威胁较小（）？

[多选题]中性粒细胞成熟障碍包括（）

[判断题]三种营养物质在胃中排空速度的快慢顺序是脂肪、糖、蛋白质。

[问答题]新时期基础教育改革对教师专业发展提出什么要求和挑战？

[单选题]卫星通信中.地球站天线仰角一般（）

[多选题]卫星地球站天线馈线系统中，同轴电缆馈线的安装工艺应符合（）要求。

[单选题]卫星地球站天线底座安装时，焊补孔洞时应使用适用于母材的焊条，每组孔眼焊补数量不得超过总数的（）

[单选题]以下哪种不是地球站天线跟踪卫星方法（）.

[单选题]地球站天线对准卫星的跟踪方法有三种，精度最高的是（）

[多选题]地球站天线跟踪卫星时，要调整的指向包括（）.

[多选题]卫星地球站天线馈线系统中，同轴电缆馈线的安装工艺应符合（）要求。

[多选题]卫星地球站天线系统的主要作用是（）

[单选题]卫星地球站天线底座安装时，焊补孔洞时应使用适用于母材的焊条，每组孔眼焊补数量不得超过总数的（）

[多选题]卫星地球站天线馈线系统中，同轴电缆馈线的安装工艺应符合（）要求。