单项选择题

Although costs are falling, wheel motors are generally more expensive than conventional drivetrains, and they don’t handle as well as conventional cars. Wheel-motor vehicles may not catch on in a big way for a decade or so, but improvements in the technology and the push for efficiency could transform ring magnets into a new standard for powering cars.
What is the reason that wheel motors will no| catch up with traditional cars soon

A. Wheel motors are more expensive and prices are still rising.
B. Wheel motors are not as easy as traditional cars to use.
C. The technology is not making improvement at present.
D. The technology cannot save as much energy as expecte

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单项选择题

The effect was temporary—temperatures started rising again after a year or so. But scientists began to wonder if the volcano hadn’t revealed a possible weapon against climate change. It takes only a back-of-the-envelope calculation to see that it would be possible to do artificially what the mountain did naturally. Ajudicious (明智的, 审慎的) application of sulfur dioxide (二氧化硫) to the upper atmosphere ,which could be accomplished by launching the gas from rockets, spraying it from high-altitude planes or releasing it from a big chimney, would have an almost immediate impact on temperature. And it would cost a thousand times less than even the most optimistic scenarios for cutting emissions. A small group of scientists began looking into how this kind of geo-engineering could be done most efficiently and with the fewest side effects. Sulfur dioxide could be applied to the upper atmosphere in all the following ways EXCEPT

A. launching the gas from rockets.
B. releasing the gas from a big chirmley.
C. producing the gas from volcanoes.
D. spraying the gas from high-altitude planes.

单项选择题

Botany, the study of plants, occupies a peculiar position in the history of human knowledge. We don’t know what our Stone Age ancestors knew about plants, but from what we can observe of preindustrial societies that still exist, a detailed learning of plants and their properties must be extremely ancient. This is logical. Plants are the basis of the food pyramid for all living things, even for other plants. They have always been enormously important to the welfare of people, not only for food, but also for clothing, weapons, tools, dyes, medicines, shelter, and many other purposes. Tribes living today in the jungle of the Amazon recognize hundreds of plants and know many properties of each. To them botany has no name and is probably not even recognized as a special branch of knowledge at all, Botany is the science that

A. studies existing tribes.
B. studies ancient way of living.
C. studies preindustrial societies.
D. studies plants.