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　　The spectacular aurora light displays that appear in Earth’s atmosphere
around the north and south magnetic poles were once mysterious phenomena. Now,
scientists have data from satellites and ground-based observations from which we
know that the aurora brilliance is an immense electrical discharge similar to
that occurring in a neon sign.

　　To understand the cause of auroras, first picture the Earth enclosed by its
magnetosphere, a huge region created by the Earth’s magnetic field. Outside the
magnetosphere, blasting toward the earth is the solar wind, a swiftly moving
plasma of ionized gases with its own magnetic filed. Charged particles in this
solar wind speed earthward along the solar wind’s magnetic lines of force with a
spiraling motion. The Earth’s magnetosphere is a barrier to the solar winds, and
forces the charged particles of the solar wind to flow around the magnetosphere
itself. But in the polar regions, the magnetic lines of force of the Earth and
of the solar wind bunch together. Here many of the solar wind’s charged
particles break through the magnetosphere and enter Earth’s magnetic field. They
then spiral back and forth between the Earth’s magnetic poles very rapidly. In
the polar regions, electrons from the solar wind ionize and excite the atoms and
molecules of the upper atmosphere, causing them to emit aurora radiations of
visible light.

　　The colors of an aurora depend on the atoms emitting them. The dominant
greenish white light comes from low energy excitation of oxygen atoms. During
huge magnetic storms oxygen atoms also undergo high energy excitation and emit
crimson light. Excited nitrogen atoms contribute bands of color varying from
blue to violet. Viewed from outer space, auroras can be seen as dimly glowing
belts wrapped around each of the Earth’s magnetic poles. Each aurora hangs like
a curtain of light stretching over the polar regions and into the higher
latitudes. When the solar flares that result in magnetic storms and aurora
activity are very intense, aurora displays may extend as far as the southern
regions of the United States.

　　Studies of auroras have given physicists new information about the behavior
of plasmas, which has helped to explain the nature of outer space and is being
applied in attempts to harness energy from the fusion of atoms.

　　1. What does the passage mainly discuss?

　　(A) The methods used to observe auroras from outer space

　　(B) The formation and appearance of auroras around the Earth’s poles

　　(C) The factors that cause the variety of colors in auroras

　　(D) The periodic variation in the display of auroras

　　2. The word "phenomena" in line 2 is closest in meaning to

　　(A) ideas

　　(B) stars

　　(C) events

　　(D) colors

　　3. The word "picture" in line 5 is closest in meaning to

　　(A) frame

　　(B) imagine

　　(C) describe

　　(D) explain

　　4. The passage describes the magnetosphere as a barrier (line 10)
because

　　(A) its position makes it difficult to be observed from Earth

　　(B) it prevents particles from the solar wind from easily entering Earth’s
atmosphere

　　(C) it increases the speed of particles from the solar wind

　　(D) it is strongest in the polar regions

　　5. The word "them" in line 16 refers to 　　(A) polar regions

　　(B) electrons

　　(C) atoms and molecules

　　(D) aurora radiations

　　-

　　6. According to the passage , which color appears most frequently in an
aurora display?

　　(A) greenish-white

　　(B) crimson

　　(C) blue

　　(D) violet

　　7. The word "emit" in line 20 is closest in meaning to

　　(A) change from

　　(B) connect with

　　(C) add to

　　(D) give off

　　8. The word "glowing" in line 22 is closest in meaning to

　　(A) shining

　　(B) moving

　　(C) charging

　　(D) hanging

　　9. Auroras may be seen in the southern regions of the United Sates when

　　(A) magnetic storms do not affect Earth

　　(B) solar flares are very intense

　　(C) the speed of the solar wind is reduced

　　(D) the excitation of atoms is low

　　10. The passage supports which of the following statements about
scientists’ understanding of auroras?

　　(A) Before advances in technology, including satellites, scientists knew
little about auroras.

　　(B) New knowledge about the fusion of atoms allowed scientists to learn
more about auroras.

　　(C) Scientists cannot explain the cause of the different colors in
auroras.

　　(D) Until scientists learn more about plasma physics, little knowledge
about auroras will be available.

　　11. Which of the following terms is defined in the passage ?

　　(A) "magnetosphere" (line 6)

　　(B) "electrons" (line 15)

　　(C) "ionize" (line 15)

　　(D) "fusion" (line 29)

　　BCBBC ADABA A

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