TOEFL Practice Test #3

<p>1. In the late 1920's, after examining the photographs of the structural appearance</p><p>2. of galaxies, Edwin P. Hubble, the American astronomer, classified the galaxies</p><p>3. into three distinct groups. These galaxies are comprised of stars that have</p><p>4. diverse structure, unequal degree of brightness, and definitely varied sizes</p><p>5. One group spirals, is highly luminous and has either a normal or a barred</p><p>6. structure. Normal spirals have two arms which radiate from the center of the</p><p>7. galaxy to the exterior edges. The two contrasting arms are enclosed in a disk</p><p>8. structure made of stars, however, in the barred structure the arms radiate</p><p>9. from the top and the bottom of a bright bar that goes through the nucleus of the</p><p>10. galaxy. Barred spirals account for nearly 25 percent of all spirals. Over two-</p><p>11. thirds of eminent, highly luminous galaxies are Spirals. The Milky Way and</p><p>12. The Andromeda are examples of spiral galaxies. Another group referred to as</p><p>13. elliptical galaxies exhibits soft, but dim brightness and has two subgroups: The</p><p>14. giant and the dwarf. While the giant elliptical galaxies have countless large</p><p>15. luminous stars, the dwarf ellipticals have a smaller number of less luminous</p><p>16. stars. Together they make up less than one-third of the galaxies. The last group</p><p>17. is the irregularly-shaped galaxies, which are non-symmetric, and their pattern is</p><p>18. rather chaotic. They account for 3% of the galaxies and their luminosity is</p><p>19. quite grainy. The Magellanic Cloud is an example of an irregularly shaped-galaxy.</p><p>Which of the following does the passage mainly discuss?</p>