主句中时态是现在完成时, have known , 时间状语要注意了。
现在完成时态的标志词如下:since+时间, for + 时段, already(肯定), yet(否定,疑问), just, before, recently, recent years, these days/years, still, lately, in the past few years, ever since, in the last five months, up to now, since then, so far, ever, never, yet, twice, once, on several occasion, in the past few days/weeks/months/years, (up to)these few days/weeks/months/years, this morning/week/month/year, up to present, up to now,till now .....
该句中符合的是B.since 1976 C.for many years(Since,,,, 和 for。。。)
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