我国探月工程二期“嫦娥三号”探测器计划于2013年年底发射,进行月球软着陆探测、

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问题:

我国探月工程二期“嫦娥三号”探测器计划于2013年年底发射,进行月球软着陆探测、月面巡视勘察、月面生存、深空测控通信与遥控操作,将把国产月球车送到月球表面。因为月球表面没有空气,且月球表面比较坚硬,所以月球车在月球表面着陆的最后阶段,月球车降落到月球表面上,需要经过多次弹跳才能停下来。假设月球车第一次落到月球表面弹起后,到达最高点时的高度为h,速度方向是水平的,速度大小是v0,月球表面重力加速度大小为g。则月球车第二次落到月球表面时的速度大小为

A.v0

B.v0+

C.

D.

考点:机械能守恒定律
题型:选择题

电阻R1和R2并联在某电源上,且R1>R2,以下说法中正确的是(  )

A.R1两端的电压大于R2两端的电压

B.R1中的电流等于R2中的电流

C.R1中的电流大于R2中的电流

D.R1中的电流小于R2中的电流

题型:选择题

若不等式-1≤x<a有4个整数解,则a的取值范围是[ ]

A.   1≤a<2    

B.   1<a<2    

C. 2<a≤3    

D. 2<a<3

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疾病预防控制机构接到甲类、乙类传染病疫情报告或者发现传染病暴发、流行时应当

A.立即报告当地卫生行政部门

B.立即报告当地人民政府

C.立即报告上级卫生行政部门

D.立即报告国务院卫生行政部门

E.立即报告省级以卜卫生行政部门

题型:选择题

American cities are similar to other cities around the world. In every country, cities reflect the values of the culture. American cities are changing, just as American society is changing.

After World War II, the population of most large American cities decreased; however, the population in many Sun Belt cities increased. Los Angeles and Houston are cities where population shifts(转移)to and from the city reflect the changing values of American society. In the late 1940s and early 1950s, city residents(居民)became wealthier. They had more children so they needed more space. They moved out of their apartments in the city to buy their own homes. They bought houses in the suburbs(郊区)。

Now things are changing. The children of the people who left the cities in the 1950s are now adults. Many, unlike their parents, want to live in the cities. They continue to move to Sun Belt cities and older ones of the Northeast and Midwest. Many young professionals are moving back into the city. They prefer the city to the suburbs because their jobs are there; or they just enjoy the excitement and possibilities that the city offers.

This population shift is bringing problems as well as benefits. Countless poor people must leave their apartments in the city because the owners want to sell the buildings or make apartments for sale instead of for rent. In the 1950s , many poor people did not have enough money to move to the suburbs; now many of these same people do not have enough money to stay in the cities.

Only a few years ago, people thought that the older American cities were dying . Some city residents now see a bright, new future. Others see only problems and conflicts. One thing is sure: many dying cities are alive again.

小题1:What does the author think of cities all over the world?

A.They are alive.

B.They are hopeless.

C.They are similar.

D.They are different.小题2:Why did American city residents want to live in the suburbs after World War II?

A.Because older American cities were dying.

B.Because they were richer and needed more space.

C.Because cities contained the worst parts of society.

D.Because they could hardly afford to live in the city.小题3:According to the 4th paragraph, a great many poor people in American cities      .

A.are faced with housing problems.

B.are forced to move to the suburbs.

C.want to sell their buildings.

D.need more money for daily expenses.小题4:We can conclude from the text that       .

A.American cities are changing for the worse.

B.people have different views on American cities.

C.many people are now moving from American cities.

D.the population is decreasing in older American cities.

题型:选择题

机组解列时,机组负荷降至()MW左右,将厂用电源由工作电源切至备用电源。

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