I have been living in the United States for twenty years but seldom so lonely as now.A. h

问题补充：

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

答案：

(答案→)A. have I felt

B. I had felt

C. I have felt

D. had I felt

解析：seldom是否定词,意为“很少”。以否定词开头的句子要进行倒装,即把助动词移至主语前。根据时间状语now可确定用现在完成时,表示从过去的某时开始一直延续到现在的情况，表示从过去到现在很少像现在那么孤独。过去完成时表示一个动作或状态在过去某一时间或动作之前已经完成或结束,即“过去的过去”。所以选项D是错误的。选项B和C不是倒装语序，应排除。