搜题请搜索小程序“爱下问搜题”
问题 选择题

现欲用浓度为5mol/L 的NaOH溶液配制 1mol/L 的NaOH溶液，应取 5mol/L的NaOH溶液与蒸馏水的体积比约为（　　）

A．1：4

B．1：5

C．2：1

D．2：3

答案

忽略稀释时体积的变化，混合后溶液体积为5mol/L的NaOH溶液与蒸馏水的体积之和．

令5mol/L的NaOH溶液与蒸馏水的体积分别为xL、yL，溶液稀释前后氢氧化钠的物质的量不变，则：

5mol/L×xL=1mol/L×（xL+yL）．

解得x：y=1：4．

故选A．

单项选择题

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.

The passage implies that until 1869, baseball was played for all of the following reasons EXCEPT________.

A．exercise

B．leisure

C．profit

D．socializing
查看答案
多项选择题

下列关于咽部先天性囊肿说法正确的是（）

A.腮裂囊肿常在扁桃体窝附近

B.舍甲囊肿常位于颈前中线区

C.咽囊囊肿常位于鼻咽顶部中线区

D.囊中边界清晰，壁薄无强化

E.囊肿在T1WI上呈低信号，T2WI上呈高信号
查看答案