GRE考试

【单选题】The polar lights known as auroras are produced when charged subatomic
Line particles, such as protons and electrons flowing from the sun throughEarth’s
magnetosphere, collide with atoms and molecules inEarth’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 theEarth 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 inEarth’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 toA．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

网考网参考答案：C
网考网解析：
The passage contains a very general description of magnetic substorms and a scientific mission to learn more about them. While the topics in answer choices A and B are discussed, they are details mentioned only in passing. There is no mention of two alternative approaches to the study of substorms (answer choice D) and the author makes no argument about the best way to conduct research in space (answer choice E). document.getElementById("warp").style.display="none"; document.getElementById("content").style.display="block"; 查看试题解析出处>>