Hi, I have a new question! Why nobody think E is right? A-->B,A cannot be practiced, so I think E is also a good answer.

Thanks!

 Since nobody answered me, I guess maybe the" as yet" in answer E is very important. Because as yet cannot represent in the future, we cannot say spraying is not advisable.

我也奇怪为什么没人考虑E...

另外，我觉得，as yet说明“到现在为止还没有”，说明不具操作性啊...

望大家指点