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 emerged of ocean currents, their patterns and the causes of them.
语法 Sentence Correction-2148
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张2865 2017-09-27 12:24:11
这里表达的意思是picture of ocean currents, pictures of their patterns and pictures of the causes of them。从句意的角度看，第一个picture of ocean currents是没有必要的，航海家早就知道大洋有很多分流，后来才知道它们的模式和原因，再重复一遍ocean currents就awkward了
