C
Uncle Sam is a tall，thin man.He‘s an older man with white hair and a white beard.He often wears a tall hat，a bow tie，and the stars and stripes of the American flag.
Who is this strange，looking man Would you believe that Uncle Sam is the US government But why do you call the US government Uncle Sam
During the War of 1812，the US government hired meat packers to provide meat to the army.One of these meat packers was a man named Samuel Wilson.Samuel was a friendly and fair man.Everyone liked him and called him Uncle Sam.
Sam Wilson stamped the boxes of meat for the army with a large US for United States.Some government inspectors came to look over Sam‘s company.They asked a worker what the US on the boxes stood for.As a joke，the worker answered that these letters stood for the name of his boss，Uncle Sam.
The joke spread，and soldiers began saying that their food came from Uncle Sam.Before long，people called all things that came from the government“Uncle Sam‘s”，“Uncle Sam”became a nickname for the US government.
Soon there were drawings and cartoons of Uncle Sam in newspapers.In these early pictures，Uncle Sam was a young man.He wore stars and stripes，but his hair was dark and he had not a beard.The beard was added when Abraham Lincoln was President.President Lincoln had a beard.
The most famous picture of Uncle Sam is on a poster from World War I.The government needed men to fight in the war.In the poster，a very serious Uncle Sam points his finger and says“I want YOU for the US Army.”
“Uncle Sam”became a________for the US government.
把10gMgCl2和MgSO4的混合物溶于适量水中，滴加2mol／L的BaCl2溶液至沉淀完全，共消耗BaCl2溶液25mL。求混合物中MgCl2和MgSO4的质量各是多少克
固定在匀强磁场中的正方形导线框abcd，各边长为1．其中ab是一段电阻为R的均匀电阻丝，其余3边均为电阻可忽略的铜线。磁场的磁感应强度为B，方向垂直纸面向里。现有一与ab段的材料、粗细、长度都相同的电阻丝PQ架在导体框上，如图所示。PQ以恒定速度方向如何
一小物块以速度v0=10m／s沿光滑地面滑行，然后沿光滑曲面上升到顶部水平的高台上，并由高台上飞出，如图所示。问当高台的高度h多大时，小物块飞行的水平距离最大这个距离是多少(g=10m／s2)
某晶体盐的水溶液呈浅绿色，在此溶液中通入氯气，溶液变为棕黄色，把所得棕黄色溶液分成两份：一份加入KSCN溶液，溶液变深红色；另一份加入BaCl2溶液，产生不溶于稀HNO3的白色沉淀，则该晶体盐的化学式是_______。
欲除去乙烷中的乙烯，可将混合气体通过盛有_______的洗气瓶；欲除去乙炔中的硫化氢，可将混合气体通过盛有_______的洗气瓶。
浓硝酸常盛装在棕色瓶中，且贮放在冷暗处，原因是_______，
碳酸氢钠溶液和烧碱溶液反应的离子方程式为_______。
常温下，氨水中存在的离子有_______。
在酸或碱存在的条件下，甲酸甲酯跟水发生水解反应的化学方程式为_______。
有下列几种气体：H2、O2、HCl、NO、NH3、CH4，其中通常情况下能用来和水做“喷泉”实验的是_______。
