We have learned English________seven years．A.sinceB.forC.inD.from
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B解析分析：for+一段时间，表示动作持续的时间长度。(延伸)1)for+一段时间，表示动作持续的时间长度，和现在完成时并不构成必然的联系。可以出现多种时态，如：He has stayed in Shanghai for half a year．(到现在为止)He stayed in America for half a year．(过去)He will stay in Beijing for half a year．(将来)He stays in New York for two months every year．(现阶段经常)He had stayed in New York for half a year before he came here．(过去的过去)2)既然for+一段时间，表示动作持续的时间长度，因此就不能和短暂性动作相连用。错：He has bee a Youth League member for three months．对：He has been a Youth League member for three months．3)since“从过去某一点时间到现在”，since后面应该跟一个“时间的点”，不能跟一段时间。但在现在完成时中for和since可以转换，如：He has stayed in Shanghai for half a year．＝He has stayed in Shanghai since half a year ago．