招标文件的内容应该包括( )。 A．施工方案 B．履约担保 C．招标公告 D．

_____ don't you get your cousin a toy?[ ]

A. What

B. How  

C. Why  

D. Which

果胶酶能分解果胶，使果汁榨取变得更容易，提高水果的出汁率。下列说法不正确的是[ ]

A．酸碱度和温度会通过影响酶来影响果汁产量

B．酶的数量越多，果汁产量越多

C．酶的催化反应时间能够影响果汁的产量

D．苹果泥的数量也能够影响果汁的产量

某企业2008年实现销售收入2480万元，全年固定成本500万元，利息70万元，变动成本率55%，所得税率25%。2008年应用税后利润弥补上年度亏损40万元，按10%提取盈余公积金，按5%提取公益金，向投资者分配的利润为可供分配利润的40%。

计算2008年的税后利润。

110kV及以上电缆敷设时，转弯处的侧压力应符合制造厂的规定；无规定时，不应大于（）

A.5kN/m

B.6kN/m

C.3kN/m

D.10kN/m

The marvelous telephone and television network that has now enmeshed the whole world, making all men neighbors, cannot be extended into space. It will never be possible to converse with anyone on another planet. Even with today’s radio equipment, the messages will take minutes—sometimes hours—on their journey, because radio and light waves travel at the same limited speed of 186, 000 miles a second.

Twenty years from now you will be able to listen to a friend on Mars, but the words you hear will have left his mouth at least three minutes earlier, and your reply will take a corresponding time to reach him. In such circumstances, an exchange of verbal messages is possible—but not a conversation.

To a culture which has come to take instantaneous communication for granted, as part of the very structure of civilized life, this "time barrier" may have a profound psychological impact. It will be a perpetual reminder of universal laws and limitations against which not all our technology can ever prevail. For it seems as certain as anything can be that no signal--still less any material object—can ever travel faster than light.

The velocity of light is the ultimate speed limit, being part of the very, structure of space and time. Within the narrow confines of the solar system, it will not handicap us too severely. At the worst, these will amount to twenty hours—the time it takes a radio signal to span the orbit of Pluto, the outer-most planet.

It is when we move out beyond the confines of the solar system that we come face to face with an altogether new order of cosmic reality. Even today, many otherwise educated men—like those savages who can count to three but lump together all numbers beyond four—cannot grasp the profound distinction between solar and stellar space. The first is the space enclosing our neighboring worlds, the planets; the second is that which embraces those distant suns, the stars, and it is literally millions of times greater. There is no such abrupt change of scale in the terrestrial affairs.

Many conservative scientists, appalled by these cosmic gulfs, have denied that they can ever be crossed. Some people never learn ; those who sixty years ago scoffed at the possibility of flight, and ten years ago laughed at the idea of travel to the planets, are now quite sure that the stars will always be beyond our reach. And again they are wrong, for they have failed to grasp the great lesson of our age— that if something is possible in theory, and no fundamental scientific laws oppose its realization, then sooner or later it will be achieved.

One day we shall discover a really efficient means of propelling our space vehicles. Every technical device is always developed to its limit and the ultimate speed for spaceships is the velocity of light. They will never reach that goal, but they will get very near it. And then the nearest star will be less than five years voyaging from the earth.

The author of the passage intends to show（）

A. the limitations of our technology

B. the vastness of the cosmic reality

C. the prospect of planetary travel

D. the psychological impact of time and space