2014年4月27日托福考前冲刺题(一)

　　Passage 1：

　　Stars may be spheres, but not every celestial object is spherical. Objects in the universe show a variety of shapes: round planets (some with rings), tailed comets,

　　wispy cosmic gas and dust clouds, ringed nebulae, pinwheel-shaped spiral galaxies,

　　Line and so on. But none of the shapes on this list describes the largest single entities in the

　　(5) universe. These are the double radio sources, galaxies with huge clouds of radio emission

　　that dwarf the visible galaxies, sometimes by a factor of a hundred or more. Stretching

　　over distances greater than a million light-years, these radio-emitting regions resemble

　　twin turbulent gas clouds, typically forming dumbbell-like shapes with the visible

　　galaxy (when it is visible) in the center.

　　(10) These double radio sources present astronomers with a puzzle. Their radio emission

　　arises from the synchrotron process, in which electrons accelerated to nearly the speed

　　of light move through magnetic fields. However, in view of the rate at which the radio

　　sources emit energy, they should disappear in a few million years as their electrons slow

　　down and case producing radiation. Somehow new electrons must be continually

　　(15) accelerated to nearly the speed of light: otherwise, by now almost none of the double

　　radio sources would be observed.

　　With the advent of high-resolution radio interferometers during the late 1970's, part

　　of the answer became clear: the electrons are produced in jets that are shot out in

　　opposite directions from the center of a galaxy. Remarkably narrow and highly directional,

　　(20) the jets move outward at speeds close to the speed of light. When the jets strike the

　　highly rarefied gas that permeates intergalactic space, the fast-moving electrons lose

　　their highly directional motion and form vast clouds of radio-emitting gas.

　　Cosmic jets have ranked among the hottest topics of astronomical research in recent

　　years as astronomers strive to understand where they come from. Why should a galaxy

　　(25) eject matter at such tremendous speeds in two narrow jets? And why are such jets not　seen in the Milky Way?

　　1. The word "celestial" in line 1 could best be  replaced by

　　(A) visible

　　(B) astronomical

　　(C) glowing

　　(D) scientific

　　2. The word "entities" in line 4 is closest in　meaning to

　　(A) factors (B) processes

　　(C) objects (D) puzzles

　　3. In the first paragraph, the author describes　objects in the universe in terms of their

　　(A) color (B) origin

　　(C) location (D) shape

　　4. According to the passage, scientists do not　fully understand why double radio sources

　　(A) have not eventually disappeared

　　(B) cannot be observed with a telescope

　　(C) are beginning to slow down

　　(D) are not as big as some planets and stars

　　5. The word "their" in line 22 refers to

　　(A) speeds

　　(B) directions

　　(C) electrons

　　(D) clouds

　　6. According to the passage, what happens when electrons and gas collide in space?

　　(A) The gas becomes more condensed.

　　(B) The gas becomes less radiated.

　　(C) The electrons disperse.

　　(D) The electrons become negatively charged.

　　7. The author suggests that astronomers consider the study of cosmic jets to be

　　(A) an obsolete scientific field

　　(B) an unprofitable venture

　　(C) an intriguing challenge

　　(D) a subjective debate

　　8. In what lines does the passage compare the　size of double radio sources with that of other　galaxies?

　　(A) Lines 4-6 (B) Lines 12-14

　　(C) Lines 19-20 (D) Lines 23-24

　　9. Where in the passage does the author mention　a technology that aided in the understanding of　double radio sources?

　　(A) Lines 2 (B) Line 7

　　(C) Line 17 (D) Line 21

　　10. The paragraph following the passage most likely discusses

　　(A) specific double radio sources

　　(B) an explanation of the synchrotron process

　　(C) possible reasons for the presence of cosmic jets

　　(D) the discovery of the first double radio sources