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问题 选择题

下列反应中属于氧化还原反应，但水既不作氧化剂又不作还原剂的是（　　）

A．2H2O

 电解 
.
 
2H2↑+O2↑

B．Cl2+H2O=HCl+HClO

C．2F2+2H2O=4HF+O2

D．2Na+2H2O=2NaOH+H2↑

答案

A、水中H元素的化合价降低，O元素的化合价升高，则属于氧化还原反应，水既作氧化剂又作还原剂，故A不选；

B、氯气中Cl元素的化合价既升高又降低，则属于氧化还原反应，但水中H、O元素的化合价均不变，则水在氧化还原反应中既不作氧化剂又不作还原剂，故B选；

C、反应中F元素的化合价降低，O元素的化合价升高，则属于氧化还原反应，水作还原剂，故C不选；

D、反应中Na元素的化合价升高，水中H元素的化合价降低，则属于氧化还原反应，水作氧化剂，故D不选；

故选B．

选择题

22. This is ____ interesting story I have ever heard.

A．by far more

B．by far the most

C．the most by far

D．the more by far
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单项选择题

Even plants can run a fever, especially when they are under attack by insects or disease. But (1) humans, plants can have their temperature (2) from 3,000 feet away—straight up. A decade ago, (3) the infrared scanning technology developed for military purpose and other satellites, physicist Stephen Paley (4) a quick way to take the temperature of crops to determine (5) ones are under stress. The goal was to let farmer (6) target pesticide spraying (7) rain poison on a whole field, which (8) include plants that don’t have the pest problem.

Even better, Paley’s Remote Scanning Services Company could detect crop problem before they became (9) to the eye. Mounted on a plane flown at 3,000 feet (10) , an infrared scanner measured the heat emitted by crops. The data were (11) into a color-coded map showing (12) plants were running "fevers". Farmers could then spot spray, using 50 to 70 percent less pesticide than they (13) would.

The bad news is that Paley’s company closed down in 1984, after only three years. Farmers (14) the new technology and long-term backers were hard (15) . But with the renewed concern about pesticides on produce, and refinements in infrared scanning, Paley hopes to (16) into operation. Agriculture experts have no doubt about the technology works. "This technique can be used (17) 75 percent of agricultural land in the United States," says George Oerther of Texas A＆M. Ray Jackson, who recently retired from the Department of Agriculture, thinks (18) infrared crop scanning could be adopted by the end of the decade. But (19) Paley finds the financial backing (20) he failed to obtain 10 years ago.

5（）

A.whose

B.which

C.what

D.where
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