集线器和交换机，（）。 A.前者分析数据报的MAC地址，后者分析其中的IP地址 B.

某医生观察某新药对预防流行性感冒的效果如下组别观察人数未发患者数发病率（%）未服药组18013027.78服药组23019017.39下列说法最合适的是（）

A.因为有抽样误差存在，不能作出结论

B.本资料应做假设检验后再作结论

C.由于未设对照组，不能认为该药预防流感有效

D.由于两组发病率相差不大，不能认为该药预防流感有效

E.服药组的发病率低于未服药组发病率，可以认为该药有效

金属-烤瓷修复体，瓷的热膨胀系数比金属的热膨胀系数

A．相差很大

B．大于

C．等于

D．小于

E．完全不同

B

If you have a bottle of water recycled from urine(尿), would you drink it? Astronauts at the ISS may soon do so.

NASA（美国航空航天局）said it would see a high-tech machine to recycle wastewater at the ISS. The machine will recycle water for washing hands, shower water, water for brushing teeth and even urine to make drinking water. It will save millions of dollars each year.

At present, each ISS astronaut uses about 4.4 liters of water every day. It costs about 24 million dollars a year to send water up to the ISS. A liter of water costs about $11,000.

The machine will be sent to the ISS later. NASA hopes it will recycle about 93% of all the water used on the station.

Will the water be clean? Different chemicals will be put in the wastewater. The water will be heated to 130℃ to kill bacteria. Scientists say that the recycled water is thousands of times better than the water from a city tap(水龙头).

50. NASA will use a high-tech machine to recycle wastewater at the ISS to ______.

A. protect the ISS                            

B. make the astronauts work harder

C. provide better water and food for the astronauts  

D. save the cost of sending water up to the ISS

51. At present it costs NASA about ___dollars to transport water up to an astronaut at the ISS a day.

A. 4.4 thousand       B. 11 thousand              C. 48.4 thousand                  D. 24 million

52. The passage mainly tells us something about ______.

A. water recycling at the ISS      B. the International Space Station

C. a high-tech machine                D. the cost of NASA

53. Which of the following sentences is TRUE?

A. The recycled water is much better than that from a city tap.

B. The high-tech machine will recycle all the water used on the station

C. The ISS astronauts use more water than us

D. The high-tech machine can only recycle urine to make water

对软盘进行写保护设置是防止软盘感染计算机病毒的有利措施之一。( )

在闭环的MRP完成对生产计划与控制的基础上的进一步扩展，将经营、财务、生产管理子系统相结合，形成（）系统。

A.闭环物料需求计划

B.制造资源计划

C.ERP

D.物料需求计划