金属基底桥架制作时，瓷层覆盖的金属基底表面应该保留多少间隙，以保证固位体与桥体表面的

阅读短文，根据短文内容回答问题。

Every year, wildfires(野火) destroy much forest land. homes are broken down, and thousands of people die. smokejumpers are stop helping to stop this.

Smokejumpers are a special kind of firefight. they jump from planes into areas that difficult to reach by car or on foot. they race to put out fires as fast as they can.

At a fire site, Smokejumpers first examine the land and decide how to fight the fire. their main goal is to stop fire from spreading. using basic tools such as shovels and axes, smokejumpers clear land of burnable material like plants and other dry material. they carry water with them too, but not much.

Although most smokejumpers are men, more women are joining. Most important are your weight and height. Smokejumpers in the U.S. for example ,must be 54 to 91 kilograms, so they don’t get hurt when they land, or get blown by strong winds.

Smokejumpers must be able to live in the wilderness. in Russia ,many smokejumpers know how to find food in the forest and even make simple furniture from trees.

They work is dangerous, the hours are long. But for these firefighters, smokejumpers isn’t just a job. They love being able to jump out of planes, fight fires, and live in the forest. As 28-year-old Russian smokejumpers Alexi Tishin says,“This is the best job for the strong and brave.”

小题1:What are Smokejumpers?

小题2:Where do the jump from?

小题3:What’s their main goal?

小题4:Why should they have proper weight?

小题5:What’s needed to be a smokejumpers?

当晶闸管装置工作在逆变状态时，若把直流电转变为某一频率或频率可调的交流电供给负载使用，则叫无源逆变或变频。

（）享有对特别行政区基本法的解释权

打开工作簿文件EX02.XLS(内容如下)，将工作表sheet1的A1：C1单元格合并为一个单元格，内容居中，计算“数量”列的“总计”项及“所占比例”列的内容(所占比例=人数/合计，最后一个单元格不计)，将工作表命名为“人力资源统计表”。

某公司人力资源统计表
人员类型	人数	所占比例
研究开发	44
工程管理	28
市场销售	22
售后服务	16
总计

(2)取“人力资源统计表”的“人员类型”列和“所占比例”列的单元格内容(不包括“合计”行)，建立“三维饼图”，数据标志为“显示百分比”，标题为“人力资源统计图”插入到表的A10：E18单元格区域内。

关于类和对象描述错误的是( )。

A．对象(Objec是现实世界中的客观事物，对象具有确定的属性

B．类是具有相同属性和行为的一组对象的集合

C．对象是类的抽象，类是对象的实例

D．类是对象的抽象，对象是类的实例