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 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.

单选题 The main purpose of the passage is to

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、 (E) demonstrate that unmanned probes are the best way to conduct research in space

【正确答案】 C

【答案解析】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).

单选题 According to the passage, all of the following are objectives of the THEMIS mission EXCEPT:

A、 predicting variations in the flux of electrons in Earth's outer radiation belt
B、 understanding how individual components of the substorm interact
C、 guaranteeing the success rates of future space missions
D、 investigating when and where substorms begin
E、 (E) understanding how substorms power the auroras

【正确答案】 C

【答案解析】This is an EXCEPT question, so your goal is to identify the one answer choice that does NOT appear in the passage. While improving the success rates of future space missions may be an outcome of the THEMIS mission, it is a possible consequence of an objective, not an objective itself. The passage does not indicate that the success rate is guaranteed. All of the other choices are listed as goals of the mission.