My grandfather 空 in the primay school for 20 years ,but he has retired and is living a peaceful
问题描述：
My grandfather 空 in the primay school for 20 years ,but he has retired and is living a peaceful
Life in the countryside now.
A taught.Bhas taught.Chad taught.Dhas been taught
答
C 后面句子是现在完成时 所以前面要用过去完成时
如果没有后面句话的话应该选D,默认爷爷是从过去一直到现在都在这个小学教书.
因为有时间for 20 years,所以不能选A,因为爷爷教书这个动作持续了20年,而不仅仅是过去的某一时刻.