下列反应的离子方程式中,正确的是( ) A.氢氧化钠溶液和醋酸反应:H++OH-

题型:选择题

问题:

下列反应的离子方程式中,正确的是(  )

A.氢氧化钠溶液和醋酸反应:H++OH-═H2O

B.用小苏打治疗胃酸过多:.C

O2-3
+2H+H2O+CO2

C.铁粉投入HCl溶液中:Fe+2H+═Fe3++H2

D.硫酸溶液与Ba(OH)2溶液反应:2H++S

O2-4+Ba2++2OH-═2H2O+BaSO4

考点:离子方程式
题型:选择题
已知椭圆的中心在原点,它在x轴上的一个焦点F与短轴的两个端点B1,B2的连线互相垂直,这个焦点与较近的长轴端点A的距离为
10
-
5
.求椭圆的方程.
题型:选择题

评标委员会提出书面评标报告后,最迟应在投标有效期结束日之前()个工作日内确定中标人。

A.15

B.20

C.10

D.30

题型:选择题

(一)


The Man of Many Secrets—Harry Houdini—was one of the greatest American entertainers in the theater next century. He was a man famous for his escapes—from prison cells, from wooden boxes floating in rivers, from locked tanks full of water. He appeared in theaters all over Europe and America. Crowds came to see the great Houdini and his "magic" tricks.
Of course, his secret was not magic, or supernatural powers. It was simply strength. He had the ability to move his toes as well as he moved his fingers. He could move his body into almost any position he wanted.
Houdini started working in the entertainment world when he was 17, in 1891. He and his brother Theo performed card tricks in club in New York. They called themselves the Houdini Brothers. When Harry married in 1894, he and his wife Bess worked together as magician and assistant. But for a long time they were not very successful. Then Harry performed his first prison escape, in Chicago in 1898. Harry persuaded a detective to let him try to escape from the prison, and he invited the local newspapermen to watch.
It was the publicity that came from this that started Harry Houdini’s success. Harry had fingers trained to escape from handcuffs and toes trained to escape ankle chins. But his biggest secret was how he unlocked the prison doors. Every time he went into the prison cell, Bess gave him a kiss for good luck—and a small skeleton key, which is a key that fits many locks, pass quickly from her mouth to his.
Harry used these prison escapes to build his fame. He arranged to escape from the local prison of every town he visited. In the afternoon, the people of the town would read about it in their local newspapers, and in the evening every seat in the local theater would be full. What was the result World-wild fame, and a name remembered today.

Which of the following is the best title for the passage

A.A Skeleton Key

B.A Man of Many Secrets

C.World-wild Fame

D.Great Escape

题型:选择题

设a0=4,a1=1,an-2=n(n-1)an,n≥2.

求幂级数[*]的和函数S(x);

题型:选择题

当陷坑发生在堤身单薄堤防临水坡时,可直接()并帮宽堤身或修筑前戗。

A.开挖

B.用黏性土填塞陷坑

C.灌浆

D.填塞软料

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