Why didn't you remind him of the possible danger?But what
网友回答
otherwise,此句使用虚拟语气.
对现在的虚拟：would + do；
对过去的虚拟：would + have done.
--Why did you leave without a word of warning to John?
为什么你不教训一下约翰就走了?
--But what could I have done otherwise?He never likes to listen to me.
不然我还能做什么呢?他从来都不听我的.
======以下答案可供参考======
供参考答案1:
A