I have been living in the United States for twenty years, but seldom so lonely as now．
A. have I felt
B. I had felt
C. I have felt
D. had I felt
网友回答
(答案→)A. have I felt
B. I had felt
C. I have felt
D. had I felt
解析：考查倒装句。否定词放在句首，使用部分倒装，题中的否定词为seldom，根据时态应用完成时态，所以助动词have 提前，选A。