Q39. Navigators have known for thousands of years that the ocean has variable currents, but it is only in the last half century that a reasonably clear picture has emerged of the patterns and causes of ocean currents. A. a reasonably clear picture has emerged of the patterns and causes of ocean currents. B. a reasonably clear picture of the patterns of ocean currents and their causes have emerged. C. a reasonably clear picture emerged of ocean currents, their patterns and the causes of them D. there have emerged a reasonably clear picture of the patterns of ocean currents and what caused them. E. there had emerged a reasonably clear picture of the patterns of ocean currents and their causes. 我选了B。答案是A。
题目用了强调结构it is ... that ... 如果还原a reasonably clear picture of the patterns of ocean currents and their causes have merged only in the last half century. 所以选B。为什么是A?
求教了!还有两天就考试了,急
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