I have been living in the United States for 20 years, but seldom ________ so lonely as now.

A．have I felt

B．I had felt

C．I have felt

D．had I felt

在成套设备交易中，除支付货款外，还有预付定金或保留金的收取。采用以下哪种支付方式与融资方式的结合最为合理？（）

A.托收与汇款

B.D/A与保理

C.信用证与托收

D.信用证与保函