问题
单项选择题
There is a real possibility that these animals could be frightened,______a sudden loud noise.
A．being there
B．should there be
C．there was
D．there having been
答案
参考答案：B
解析： 21．此句为与现在事实相反的虚拟句，且后部分用倒装形式，还原后即为if there should be a sudden loud noise。
，乙图中通过R的电流为
。已知
，则
