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
1. 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. 2. The sun is 93 million miles from the earth. Yet we
can use energy from the sun because electromagnetic energy travels through
space. 3. 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. 4. 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. 5. 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).
6. 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 3 ______