Data from the pioneer spacecraft of the National Aeronautics and Space Administration (NASA) 11 prove the theory that the burning 900-degree Fahrenheit surface temperature of Venus is 12 to an atmospheric greenhouse effect caused mainly by a blanket of carbon dioxide. Such a greenhouse effect is created when energy in the form of sunlight easily passes through a planet's atmosphere, warms its surface, and is 13 to heat radiation that is then held in by the atmosphere. The orbiting spacecraft 14 Venus' atmosphere from top to 15 , enabling NASA'S scientists to establish the exact amount of sunlight absorbed at various places in the planet's atmosphere and on its surface. Measurements of atmosphere composition, temperature profiles, and radiative heating predicted Venus' surface temperature very 16 . The planet is closer to the Sun than is Earth, and it has a relatively thin atmosphere, but Venus' atmosphere consists of more than ninety percent carbon dioxide, 17 to less than four percent in that of Earth. Because of its 18 percentage of carbon dioxide, Venus' atmosphere traps much more heat radiation than does Earth's. Thus, the Venus studies are 19 to be important to the understanding of possible adverse effects on Earth's agriculture and sea 20 that could result from the long-term use of fossil fuels, which add carbon dioxide to the atmosphere.

　　A.  levels      B. converted   C.    accurately       D.    simplified
　　E. owing F. conveyed    G.    bottom    H.    sampled
　　I.  due   J. higher  K.    vainly     L.    compared
　　M. end    N. believed     O.    apparently

　　答案：11.   O   12.  I     13. B    14. H   15. G   16. C   17. L    18. J     19. N   20. A