下面的短文后有2项测试任务：(1)第23～26题要求从所给的6个选项中为第3～6段每段选择1个最佳标题：(2)第27～30题要求从所给的6个选项中为每个句子确定1个最佳选项。 Electromagnetic Energy
White light seems to be a combination of all colors. The energy that comes
from a source of light is not limited to the kind of energy you can see. Heat is
given off by a flame or an electric light. On a cloudy day it is possible to get
a sunburn even though you feel cool. Visible light and the kind of energy that
produce warmth and sunburn are examples of electromagnetic energy.
The sun is 93 million miles from the earth. Yet we can use energy from the
sun because electromagnetic energy travels through space. Many
other kinds of energy are also types of electromagnetic energy. Radio,
television, and radar signals travel from transmitters to receivers as
low-energy electromagnetic waves. Infrared (红外线的) radiation is an
electromagnetic wave. When it is absorbed by matter, heat is produced. Waves of
infrared and visible light have more energy than waves of radio, television, or
radar. Ultraviolet rays (紫外线) and X-rays are electromagnetic waves with even
greater amounts of energy. Infrared radiation is used in cooking food and
heating buildings. Sunlight and electric lights are part of our requirements for
normal living. Ultraviolet radiation is useful in killing certain disease
organisms. X-rays and gamma rays have so mush energy that they travel right
through solid objects. They can be used to detect and treat cancer. X-rays are
used in industry to find hidden cracks in metal, and in medicine to reveal
broken bones. Usually we use electricity to generate
electromagnetic energy. The source of most of our energy is the sun. Heat from
the sun causes water to evaporate. When the water falls to the earth as rain,
some of it is trapped behind dams and then used to operate electric generators.
Other generators are powered by coal, but the energy stored in coal came from
the sun, too. Until recently, the source of the tremendous
amount of energy given off by the sun was a puzzle. If the sun depended on
chemical reactions, it would have used up all its energy long ago. Experiments
with electromagnetic radiation led to the theory that mass can be converted into
energy. About forty years after the theory was proposed, nuclear energy was
harnessed (利用) by man. Chemical energy comes from electron (电子) rearrangement.
Nuclear energy comes from a change in the nucleus of an atom. Compared with
chemical reactions, nuclear reactions release millions of times more energy per
pound of fuel. We now believe that the sun’s energy comes from the nuclear
reactions in which hydrogen is changed into helium(氦). Nuclear
energy is beginning to compete with coal as an economical source of power to
generate electricity. It is also being used to operate engines in large ships.
Scientists continue to seek new and better methods of obtaining and using
energy.
A. Nuclear Reactions as the Lasting Source of the Sun’s
Energy B. The Most Important Source of Energy C.
Types of Electromagnetic Energy D. X-rays Are Used to Detect and
Treat Cancer. E. Seeking New Sources of Energy
F. Nuclear Energy is Beginning to Compete with Coal Paragraph 6 ______