下列哪项不是尿路感染的易感因素（） A.前列腺肥大 B.尿路结石 C.留置导尿 D.

在实验室测定碳酸钠与碳酸氢钠的混合物中，碳酸钠的质量分数[用符号w(Na₂CO₃)表示]，称取此混合物5.lg，溶于水中，配成250mL溶液。

a．(10分)方案一：沉淀法测w(Na₂CO₃)利用化学反应把HCO₃^－、CO₃^2－完全转化为沉淀，称取沉淀的质量，由此计算混合物中w (Na₂CO₃)。

（1）量取100 mL配制好的溶液于烧杯中，滴加足量沉淀剂，把溶液中HCO₃^－、CO₃^2－完全转化为沉淀，应选的试剂是___________ （填编号）。

A．CaCl₂

B．MgSO₄

C．．NaCI

D．Ba(OH)₂（2）简述证明HCO₃^－、CO₃^2－已完全沉淀的实验操作_________________________。

（3）过滤，提取沉淀，则过滤操作所需要的玻璃仪器有________________________。

（4）洗涤沉淀，简述洗涤沉淀的操作_____________________________。

（5）干燥充分，称取沉淀的质量为9.8g，由此计算w(Na₂CO₃)。如果此步中，沉淀未干燥充分就称量，则测得w (Na₂CO₃)________________（填偏大或偏小、无影响）。

b．方案二：滴定法测w(Na₂CO₃)量取25.00 mL配制好的溶液加入锥形瓶中，滴加2滴酚酞试剂，摇匀，用0.2000 mol/L的盐酸进行滴定到终点。重复此操作2次，消耗盐酸的体积平均值为20.00 mL。      [已知饱和的碳酸溶液PH为3.9]

（1）量取25.00 mL配制好的溶液，应选择_______________仪器来完成。

（2）判断滴定终点的依据是_____________________，此过程中反应的离子方程式为__________________________________________________。

（3）此法测得w(Na₂CO₃)=________%（保留两位小数）

There has been much speculation about the origin of baseball. In 1907 a special commission decided that the modern game was invented by Abner Doubleday in 1839. One hundred years later the National Baseball Museum was opened to honor Doubleday. Historians, however, disagree about the origin of baseball. Some say that baseball comes from bat-and-ball games of ancient times. It is a matter of record that in the 1700s English boys played a game they called "baseball". Americans have played a kind of baseball since about 1800. At first the American game had different rules and different names in various parts of the country — "town ball", "rounders", or "one old cat". Youngsters today still play some of these simplified forms of the game.Baseball did not receive a standard set of rules until 1845, when Alexander Cartwright organized the Knickerbocker Baseball Club of New York City. The rules Cartwright set up for his nine-player team were widely adopted by other clubs and formed the basis of modern baseball. The game was played on a "diamond" infield with the bases 90 feet apart. The first team to score 21 runs was declared the winner. By 1858 the National Association of Baseball Players was formed with 25 amateur teams. The Cincinnati Red Stockings began to pay players in 1869.

Which of the following is true about the origins of baseball

A．Historians agree that baseball was invented by Abner Doubleday.

B．Baseball, as played in the early 19th century, differed very little from today’s game.

C．As early as the 1700s, English boys played a game called "baseball".

D．The first standard set of baseball rules was established at the turn of the century.

安全边际率等于( )。

A．销售利润除以变动成本率
B．盈亏临界点作业率乘边际贡献率
C．销售利润率除以边际贡献率
D．边际贡献率乘变动成本率

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