1、第 第 頁英語的閱讀題練習(xí)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 d

2、isappear in a few million years as their electrons slow down and cease producing radiation。Somehow new electrons must be continually accelerated to nearly the speed of light，otherwise，by now almost none of the double radio sources would be observed。With the advent of highresolution radio interferome

3、ters during the late 1970s，part of the answer became clear：the electrons are produced in jets that are shot out in opposite directions from the center of gala*y。Remarkably narrow and highly directional，the jets move outward at speeds close to the speed of light。When the jets strike the highly rarefi

4、ed gas that permcales intergalactic space，the fastmoving electrons lose their highly directional motion and form vast clouds of radioemitting 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 sho

5、uld a gala*y eject matter at such tremendous speeds in two narrow jets？And why are such jets not seen in the Milky Way？9。The word celestialin line 1could best be replaced byAvisibleBastronomicalCglowingDscientific10。The word entitiesin line 4is closest in meaning toAfactorsBprocessesCobjectsDpuzzles11。In the first paragraph，the author