Because American parents believe that knowledge leads to a meaningful life, they try to gi
A.worth
B.worthy
C.valuable
D.worthwhile
A.worth
B.worthy
C.valuable
D.worthwhile
A.tedious
B.irritable
C.worrying
D.disinteresting
A.To keep out boats that are too large for the canal.
B.To measure the tonnage of canal boats.
C.To load and unload the cargo.
D.To change the depth of the watch
A.change people' s conservative attitudes towards their lifestyles
B.help young people make friends with the opposite sex
C.help them achieve success in their interpersonal relationships
D.make them competitive in the job market
A.They are well educated.
B.They all have a good job.
C.They take a pessimistic attitude towards life.
D.They are not satisfied with their jobs.
A.Movies with sound.
B.Nylon.
C.The radio.
D.The computer.
An astronomer first reported the matter after noting some unusual behaviour in visible matter. In 1993, Swiss astrophysicist Fritz Zwicky concluded that 【C2】______ was causing strange gravitational effects【C3】______ these galaxies.
Galaxies are like【C4】______ islands in deep space【C5】______ billions of stars that are held together by the force of【C7】______ .Some galaxies are part of【C6】______ systems called clusters; which contain many galaxies. Most galaxies; belong to smaller systems called groups. Groups and clusters in 【C8】______ form. even larger【C9】______ known as super-clusters. Just【C10】______ the force of gravity keeps stars together in galaxies the force of gravity【C11】______to keep galaxies together in clusters~
This same force of gravity keeps planets【C12】______ around the sun【C13】______ flying off into space. How great a force gravity exerts depends on the mass of the objects【C14】______ and the distance between them, a【C15】______ discovered by Newton. The amount of mass and the distance between objects also【C16】______ how fast the objects travel as they orbit each other. The force of its gravity keeps Earth and the other planets【C17】______ orbit around it. The orbital speeds of the planets【C18】______ with increasing distance from the sun. The planet nearest to the sun travels at an orbital speed of 48 kilometers per second【C19】______ the distant planet Pluto orbits【C20】______ speed of 7 kilometers per second
【C1】
A.visible
B.invisible
C.perceived
D.tangible
A.angry
B.indifferent
C.overjoyed
D.worried
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