单项选择题

Solid fuel rockets are expensive to operate because of their ______.

A．size
B．fuel
C．construction
D．complicated engines
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问答题
Europe was the first of the major world regions to develop a modern economy based on commercial agriculture and industrial development. Its successful modernization can be traced to the continent’s rich endowment of economic resources, its history of innovations, the evolution of a skilled and educated labor force, and the interconnectedness of all its parts--both naturally existing and man-made--which facilitated the easy movement of massive quantities of raw materials and finished goods and the communication of ideas. Europe’s economic modernization began with a marked improvement in agriculture output in the 17th century, particularly in England. The traditional method of cultivation involved periodically allowing land to remain fallow; this gave way to continuous cropping on fields that were fertilized with manure nom animals raised as food for rapidly expanding urban markets. Greater wealth was ac- cumulated by landowners at the same time that fewer farmhands were needed to work the land. The accumulated capital and abundant cheap labor created by this revolution in agriculture fueled the development of the Industrial Revolution in the 18th century. The revolution began in northern England in the 1730s with the development of water-driven machinery to spin and weave wool and cotton. By mid-century James Watt had developed a practical steam engine that emancipated machinery from sites adjacent to waterfalls and rapids. Britain had been practically deforested by this time and the incessant demand for more fuel to run the engines led to the exploitation of coal as a major industry. Industries were built on the coalfields to minimize the cost of transporting coal over long distances. The increasingly surplus rural population flocked to the new manufacturing areas. Canals and other improvements in the transportation infrastructure were made in these regions, which made them attractive to other industries that were not necessarily dependent on coal and thus prompted development in adjacent regions Industrialization outside of England began in the mid-19th century in Belgium and northeastern France and spread to Germany, The Netherlands southern Scandinavia and other areas in conjunction with the construction of railways. By the 1870s the governments of the European nations had recognized the vital importance of factory production and had taken steps to encourage local development through subsidies and tariff protection against foreign competition. Large areas, however, remained virtually untouched by modern industrial development, including most of the Iberian Peninsula southern Italy, and a broad belt of eastern Europe extending from the Balkans on the south to Finland and northern Scandinavia. During the 20th century Europe has experienced periods of considerable economic growth and prosperity, and industrial development has proliferated much more widely throughout the continent: but continued economic development in Europe has been handicapped to a large degree by its multi- national character--which has spawned economic rivalries among states and two devastating World wars--as well as by the exhaustion of many of its resources and by increased economic, competition from overseas. Governmental protectionism, which has tended to restrict the potential market for a product to a single country, has deprived many industrial concerns of the efficiencies of large-scale production serving a mass market ( such as is found in the United States). In addition, enterprise efficiency has suffered from government support and from a lack of competition within a national market area. Within individual countries there have been growing tensions between regions that have prospered and those that have not. This core-periphery problem has been particularly acute in situations where the contrasting regions are inhabited by different ethnic groups.
单项选择题
The author tells us that
A．whether a liquid-fuel or a solid-fuel rocket is better depends on the purpose
B．neither type is superior
C．forty years ago, large solid-fuel rockets with solid fuels as powerful as liquid fuels were made
D．the thrust can be made to vary by adjusting the direction of the pump
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