2011大学英语四级考试试题及参考答案5

 A） They may have been caused by the damage to the radio systems. B） They may have taken place during take?off and landing. C） They were proved to have been caused by the passengers' portable computers. D） They were suspected to have resulted from electromagnetic interference. 23.Few airlines want to impose a total ban on their passengers using electronic devices because_______. A） they don't believe there is such a danger as radio interference B） the harmful effect of electromagnetic interference is yet to be proved C） most passengers refuse to take a plane which bans the use of radio and cassette players D） they have other effective safety measures to fall back on 24.Why is it difficult to predict the possible effects of electromagnetic fields on an airplane's computers？

    A） Because it is extremely dangerous to conduct such research on an airplane. B） Because it remains a mystery what wavelengths are liable to be interfered with. C） Because research scientists have not been to produce the same effects in labs. D） Because sxperts lack adequate equipment to do such research. 25.It can be inferred from the passage that the author_______. A） is in favor of prohibiting passengers' use of electronic devices completely B） has overestimated the danger of electromagnetic interference C） hasn't formed his own opinion on this problem D） regards it as unreasonable to exercise a total ban during flight Questions 26 to 30 are based on the following passage：The rise of multinational corporations （跨国公司）， global marketing， new communi cations technologies， and shrinking cultural differences have led to an unparalleled increase in global public relations or PR. Surprisingly，since modern PR was largely an American invention，the U.S.leader ship in public relations is being threatened by PR efforts in other countries.Ten years ago， for example， the world's top five public relations agencies were American?owned. In 1991， only one was. The British in particular are becoming more sophisticated and creative. A recent survey found that more than half of all British companies include PR as part of their corporate （公司的） planning activities， compared to about one?third of U.S. companies， It may not be long before London