[单项选择]The need for solar electricity is clear. It is safe, ecologically sound, efficient, continuously available, and it has no moving parts. The basic problem with the use of solar photovoltaic devices is economics, but until recently very little progress had been made toward the development of low-cost photovoltaic devices. The larger part of research funds has been devoted to the study of single crystal silicon solar cells, despite the evidence that this technique holds little promise. The reason for this pattern is understandable and historical. Crystalline silicon, however, is particularly unsuitable to terrestrial solar cells.
Crystalline silicon solar cells work well and are successfully used in the space program, where cost is not an issue. While single crystal silicon has been proven in extraterrestrial use with efficiencies as high as 18 percent, and other more expensive and rare materials can have even higher efficiencies, costs must be reduced by a factor of more than 100 to
A. the advantages of solar cells
B. the efficiencies of solar cells
C. how solar cells are manufactured
D. in what ways solar cells are used

[单项选择]The need for solar electricity is clear, it is safe, ecologically sound, efficient, continuously available, and is has no moving parts. The basic problem with the use of solar photovoltaic devices is economics, but until recently very little progress has been made toward the development of low-cost photovoltaic devices. The larger part of research funding has been devoted to study of single-crystal silicon solar cells, despite the evidence, including that of the leading manufacturers of crystalline silicon, that the technique holds little promise. The reason for this pattern is understandable and historical. Crystalline silicon is the active element in the very successful semiconductor industry, and virtually all of the solid state devices contain silicon transistors and diodes. Crystalline silicon, however, is particularly unsuitable to terrestrial solar cells.
Crystalline silicon solar cells work well and are successfully used in the space program, where cost is not an issue. Wh
A. discussing the importance of solar energy
B. explaining the functioning of solar cells
C. presenting a history of research on energy sources
D. describing a possible solution to the problem of the cost of photovoltaic cells

[单项选择]The need for solar electricity is clear. It is safe, ecologically sound, efficient, continuously available, and is has no moving parts. The basic problem with the use of solar photovoltaic devices is economics, but until recently very little progress has been made toward the development of low-cost photovoltaic devices. The larger part of research funding has been devoted to study of single-crystal silicon solar cells, despite the evidence, including that of the leading manufacturers of crystalline silicon, that the technique holds little promise. The reason for this pattern is understandable and historical. Crystalline silicon is the active element in the Very successful semiconductor industry, and virtually all of the solid state devices contain silicon transistors and diodes. Crystalline silicon, however, is particularly unsuitable to terrestrial solar cells.
Crystalline silicon solar cells work well and are successfully used in the space program, where cost is not an issue. Wh
A. discussing the importance of solar energy
B. explaining the functioning of solar cells
C. presenting a history of research on energy sources
D. describing a possible solution to the problem of the cost of photovoltaic cells