The concept of solar power satellites, or SPS, first put forward in the 1960s, is still not widely known by the general public. For example, at many public exhibitions about energy, SPS is not even mentioned. This is mainly because very little money has been spent on SPS research
There are people who claim that SPS is unrealistic － because launch costs are much too high today; or because it is too far away. So why do we believe that it is important to continue to do researches on SPS? The reason is very simple.
Humans are going to need huge amounts of electric power in coming decades. Within 50 years the world population is expected to double, while economic growth will continue around the world, especially in the poorer countries. But existing energy sources already face serious problems. They are limited; they are polluted; they are dangerous. So 50 or 100 years from now, where is our power going to come from? Nobody knows. And so we believe that new large-scale possibilities should be studied further.
We must remember that humans have some choices concerning our future. To some extent we can choose the direction in which our civilization develops. And choices that are made in the coming decades － such as the energy sources that we will or will not use, will have major, long-term meaning for human life on earth. We believe that if research continues to show that SPS is environmentally and economically attractive, SPS will open the door to a much more attractive future for human civilization than any ground-based energy source, and one that the public will support and that young people will find challenging and exciting. Furthermore energy from SPS can be readily used in developing countries, as the SPS 2000 project will show, thus aiding economic development worldwide. In addition, by creating large commercial fund for space engineering, SPS will open the frontier of space to economic development, thus creating a limitless new field for the growth of the world economy.
小题1:Which of the following may be the best title for the passage?
A．The Future Energy－ SPS
B．The Concept of SPS
C．Humans and SPS
D．Advantages of SPS小题2:Which of the following statements about SPS is TRUE?
A．The research on SPS started in the 1960s is still not appreciated by the public.
B．The research is showing SPS can benefit environment and economy at present.
C．The energy from SPS is now being used in some developing countries.
D．The public don’t know about SPS because little time is devoted to the research.小题3:Paragraph 3 mainly talks about ______.
A．the present serious energy problems
B．where to get energy sources in the future
C．the importance of controlling world population
D．the need to explore new energy sources小题4:The writer’s attitude towards the research can best be summarized by the saying “______”.
A．In time of peace prepare for war
B．Put the cart before the horse
C．One man’s meat is another man’s poison
D．Easier said than done
仅与曲线C的起止点有关，而与曲线C的形状无关，则该单值标量场的梯度是一个（）矢量场。