问题补充:
For many years, people electric cars. However, making them has been more difficult than predicted.
A. dream of
B. had dreamed of
C. dreamed of
D. have dreamed of
答案:
A. dream of
B. had dreamed of
C. dreamed of
(答案→)D. have dreamed of
解析: 考查时态。根据时间状语For many years,可知应用现在完成时态。所以选D。