TAILIEUCHUNG - 1995-2000 Reading Full Test phần 7

Tham khảo tài liệu '1995-2000 reading full test phần 7', ngoại ngữ, ngữ pháp tiếng anh phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | D harvesting squash. 7. The word disaster in line 22 is closest in meaning to A control B catastrophe C avoidance D history 8. According to the passage the Mandans preserved their food by A smoking B drying C freezing D salting 9. The word it in line 25 refers to A June B corn C time D squash 10. Which of the following crops was cultivated primarily by men A Corn B Squash C Sunflower D Tobacco 11. Throughout the passage the author implies that the Mandans A planned for the future B valued individuality C were open to strangers D were very adventurous Questions 12-20 The elements other than hydrogen and helium exist in such small quantities that it is accurate to say that the universe somewhat more than 25 percent helium by weight and somewhat less than 25 percent hydrogen. Astronomers have measured the abundance of helium throughout our galaxy and in other galaxies as well. Helium has been found in old stars in relatively young ones in interstellar gas and in the distant objects known as quasars. Helium nuclei have also been found to be constituents of cosmic rays that fall on the earth cosmic rays are not really a form of radiation they consist of rapidly moving particles of numerous different kinds . It doesn t seem to make very much difference where the helium is found. Its relative abundance never seems to vary much. In some places there may be slightly more of it In others slightly less but the ratio of helium to hydrogen nuclei always remains about the same. Helium is created in stars. In fact nuclear reactions that convert hydrogen to helium are responsible for most of the energy that stars produce. However the amount of helium that could have been produced in this manner can be calculated and it turns out to be no more than a few percent. The universe has not existed long enough for this 141 figure to he significantly greater. Consequently if the universe is somewhat more than 25 percent helium now then it must have been about 25 percent helium at a time .

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