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　　Questions 21 to 25 are based on the following passage:

　　21. The passage implies that the telegraph cable was built mainly _________.

　　A) for oceanographic studies

　　B) for military purposes

　　C) for business considerations

　　D) for investigating the depths of the oceans

　　22. It was ________ that asked Maury for help in oceanographic studies.

　　A) the American Navy

　　B) some early intercontinental travellers

　　C) those who earned a living from the sea

　　D) the company which proposed to lay an undersea cable

　　23. The aim of voyages Maury encouraged in the 1840s was __________.

　　A) to make some sound experiments in the oceans

　　B) to collect samples of sea plants and animals

　　C) to estimate the length of cable that was to be made

　　D) to measure the depths of two oceans

　　24. 'Defied' in the 5th paragraph probably means ________

　　A) 'doubted' B) 'gave proof to'

　　C) 'challenged' D) 'agreed to'

　　25. This passage is mainly about _________

　　A) the beginnings of oceanography

　　B) the laying of the first undersea cable

　　C) the investigation of ocean depths

　　D) the early intercontinental communications