PART Ⅲ CLOZE Decide which of the choices given below would correctly complete the passage if inserted in the corresponding blanks. Mark the correct choice for each blank on the ANSWER SHEET.
Mounting evidence has led astronomers to just an improbable conclusion; At least 90 percent and possibly 99 percent of all matter in the universe is completely 1 . Astronomers call this stuff dark matter.
An astronomer first reported the matter after noting some unusual behaviour in visible matter. In 1993, Swiss astrophysicist Fritz Zwicky concluded that 2 was causing strange gravitational effects 3 these galaxies.
Galaxies are like 4 islands in deep space 5 billions of stars that are held together by the force of 6 . Some galaxies are part of 7 systems called clusters; which contain many galaxies. Most galaxies; belong to smaller systems called groups. Groups and clusters in 8 form even larger 9 known as super-clusters. Just 10 the force of gravity keeps stars together in galaxies the force of gravity 11 to keep galaxies together in clusters~
This same force of gravity keeps planets 12 around the sun 13 flying off into space. How great a force gravity exerts depends on the mass of the objects 14 and the distance between them, a 15 discovered by Newton. The amount of mass and the distance between objects also 16 how fast the objects travel as they orbit each other. The force of its gravity keeps Earth and the other planets 17 orbit around it. The orbital speeds of the planets 18 with increasing distance from the sun. The planet nearest to the sun travels at an orbital speed of 48 kilometers per second 19 the distant planet Pluto orbits 20 speed of 7 kilometers per second PART Ⅳ GRAMMAR AND VOCABULARY There are 30 sentences in this section. Beneath each sentence there are four words or phrases marked A) , B) , C), and D). Choose one word or phrase that correctly completes the sentence.