阅读下面的短文，文中有15处空白，每处空白给出4个选项。请根据短文的内容，从4个选项中选择1个最佳答案。 Solar equipment Since about 1800,
near the beginning of the Industrial Revolution, coal, petroleum, and gas have
been used at a rapidly increasing rate. The supply of these (51)
is limited, and electric power is very scarce in many places. Some
scientists believe solar energy is the only (52) which can
meet the world’s enormous (53) for power. Great progress had
been made in harnessing the sun. Not (54) is the sun now
used in cooking, but it also supplies power for (55) things
as beacon lights for ships and airplanes. It operates telephone lines, portable
radios, electric clocks, hearing aids, and (56)
communication satellites. Some homes and office buildings in the United States
are now being (57) with solar energy. The
three most significant types of solar equipment so (58) are
the furnace, the still, and the cell. Solar furnaces heat water or air,
(59) is then circulated through a building to make it
comfortable. Solar stills are (60) important because they
can provide (61) water at a relatively cheap rate. Salt can
be easily removed from sea water with a solar still. The most
highly developed is the solar cell. Some cells are so (62)
that they can turn 16 percent of the energy they received from the sun into
electric energy. One of the cell’s biggest advantages is (63)
it can be made either small enough to carry (64)
large enough to produce a current that can run an automobile. Besides, it has a
very long life. It is still too expensive for the average consumer. But when
ways are (65) to produce it more cheaply, we can expect its
use to be widespread.