2. 外语
  3. The polar lights known as auroras are produced when charged subatomic Line particles, such as protons and electrons flowing fro

The polar lights known as auroras are produced when charged subatomic Line particles, such as protons and electrons flowing fro

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问题       The polar lights known as auroras are produced when charged subatomic
Line  particles, such as protons and electrons flowing from the sun through Earth’s
      magnetosphere, collide with atoms and molecules in Earth’s upper atmosphere.
      For reasons not entirely understood, magnetic storms, called substorms,
(5)   occasionally occur where the flow of particles greatly increases and the
      interplanetary magnetic field becomes much stronger. These substorms are frequently
      visible on the Earth because they increase the intensity of the polar lights.
           Recently, five identical probes were blasted into orbit in a $200 million US
      project known as the THEMIS mission. Scientists hope the probes will be able to
(10)  investigate a number of mysteries about the nature of the substorm instabilities,
      including when and where substorms begin, how the individual components
      of the substorm interact, and how substorms power the auroras. The mission’s
      secondary objectives involve understanding and predicting variations in the flux
      of electrons in Earth’s outer radiation belt. These electrons pose a hazard to the
(15)  safety of both astronauts and spacecraft. Understanding substorm instabilities
      would thus improve success rates of future space missions.
The main purpose of the passage is to
选项 A、explain why it is important to invest in space research
B、explain how magnetic substorms interfere with satellite communications
C、define magnetic substorms and identify a recent scientific experiment to study them
D、compare two alternative approaches to the study of magnetic substorms
E、demonstrate that unmanned probes are the best way to conduct research in space
答案C
解析
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