youwouldlaughifanyone...下面这句话是虚拟语气吗?youwouldlaughifanyoneshouldaskyouwhetheryoucantellananimalfromaplant.从句为什么要用should而不是别的什么动词过去式youwouldlaughifanyoneshouldas

　　youwouldlaughifanyone...下面这句话是虚拟语气吗?

　　youwouldlaughifanyoneshouldaskyouwhetheryoucantellananimalfromaplant.

　　从句为什么要用should而不是别的什么动词过去式youwouldlaughifanyoneshouldaskyouwhetheryoucantellananimalfromaplant，这句话中的should如果换成would或者换成asked有什么区别呢？