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16. Towards the end of the 19th century the larger companies _more and more on mass advertising to promote their new range of products. The market during this period _by a small number of giant, conglomerate enterprises. a) relied, has been controlled b) relied, had been controlled c) were relying, has been controlled d) relied, were controlled 17. To cater for the fitness boom of the 80s and provide the up-to-date facilities people want, over 1,500 private health and fitness clubs_during the past 15 years. a) were built c) have been built b) had been built d) will be built 18. In 1936 the British Broadcasting Corporation_to provide a public radio service. Since then the BBC _by the establishment of independent and commercial radio and television, which_the BBC's broadcasting monopoly. a) was established, was influenced, removed b) was established, has been influenced, removed c) was established, has been influenced, had removed d) was established, had been influenced, removed 19. The Neolithic Age was a period of history which_ in approximately 6000 B. C. and_until 3000 B. C. a) began, lasted c) began, was lasting b) had begun, lasted d) had begun, had been lasting 20. A major problem in the construction of new buildings is that windows_while air conditioning systems a) have been eliminated, have not been perfected b) were eliminated, were not perfected c) had been eliminated, had not been perfected d) eliminate, are not perfected