情景一：你有一本极好的数学复习用书，同学向你借这本书。 情景二：期中考试前，学习

Fear seems to be the dominant mood of the moment. Hurricanes, tidal waves, floods, earthquakes and terrorism this year have all brought with them not only appalling scenes of devastation, death and suffering, but also outrage at the lack of preparations to avoid or cope with these disasters. Now even the birds of the air are a threat, we are told. That migrating flock visible On the horizon at sunset, once a consoling reminder of the eternal rhythms of nature, could be carrying the virus which might soon kill tens of millions of people.

Given the many fingers pointed at governments in the wake of other disasters this year, it is hardly surprising that they are scrambling to respond to the threat posed by avian influenza. After confirmation this week that the HSN1 strain of bird flu, which has been spreading quickly in Asia, had been discovered in Romania and perhaps Greece, European Union foreign ministers convened an emergency meeting. President George Bush, still smarting from a torrent of criticism of his government’s clumsy response to Hurricane Katrina, has promised to rush out emergency plans for dealing with an outbreak of pandemic flu which have been stalled for years. Countries around the world are hurrying to stockpile the only current antiviral drug, Tamifln, which might be effective in saving lives in any pandemic or curbing its spread. The World Health Organisation is calling for an internationally coordinated effort. Health ministers from around the globe are due to meet next week in Canada to discuss what steps to take.

Is any of this eff6rt justified Or are politicians simply helping to feed public panic, and then covering themselves by promising to spend lavishly against a threat which may never materialize and to reduce a risk which they do not understand To ask these questions is not to counsel complacency, but to apply the kind of test which is required in any kind of disaster planning, not least because the world is an inherently dangerous place and it is impossible to plan against every possible disaster. With the media full of warnings of impending mass death, an overreaction is all too possible.

According to the text, American emergency plans for coping with an outbreak of pandemic flu （）

A. have been stipulated

B. have been enacted

C. have been abolished

D. have been delayed

体力活动可使其发生的危险性减少的是（）

A.胃癌

B.肝癌

C.鼻咽癌

D.乳腺癌

E.结肠癌

请你写出一个含字母x，并且当x≤2时在实数范围内有意义的二次根式（    ）。

（18分）利用水流和太阳能发电，可以为人类提供清洁能源。水的密度 ，太阳光垂直照射到地面上时的辐射功率 ，地球表面的重力加速度取g=10m／s²。

（1）三峡水电站发电机输出的电压为18kV。若采用500kV直流电向某地区输电5.0×10⁶kW，要求输电线上损耗的功率不高于输送功率的5％，求输电线总电阻的最大值；

（2）发射一颗卫星到地球同步轨道上（轨道半径约为地球半径的6.6 ）利用太阳能发电，然后通过微波持续不断地将电力输送到地面，这样就建成了宇宙太阳能发电站。求卫星在地球同步轨道上向心加速度的大小；

（3）三峡水电站水库面积约1.0×10⁹m²，平均流量Q=1.5×l0⁴m³／s，水库水面与发电   机所在位置的平均高度差h=l00m，发电站将水的势能转化为电能的总效率 。在地球同步轨道上，太阳光垂直照射时的辐射功率为10P₀。太阳能电池板将太阳能转化为电能的效率 =20％，将电能输送到地面的过程要损失50％。若要使（2）中的宇宙太阳能发电站的发电能力与三峡电站相当，卫星上太阳能电池板的面积至少为影大?

在同步串行通信中，HDLC是 【14】 的简写。