当发现射水抽气器的水箱水位过低时，应先（）
A.及时补水
B.检查放水门
C.汇报有关人员
D.可维持运行
参考答案：A
For many years, people （）electric cars. However, making them has been more difficult that predicted.
A. had dreamed of
B. have dreamed of
C. dreamed of
D. dream of
