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ManhattanGMAT Staff 对于1997在1981年后却用过去完成的解释: in this case, 1981 is actually, irritatingly enough, irrelevant. the only relevant places on the proverbial timeline are (a) when the number of hours started growing (this is the 'earlier event' or FIRST time marker), and (b) 1997 (the SECOND past time marker). because 1997 is in the past, and the 'arrow of relevance' points to / stops at 1997, you use the past perfect. if we were talking about a modern statistic instead ("as of today, the number has grown to..."), then we'd use the present perfect. |
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