If you should have any difficulty,please ring me up为什么是虚拟语气

虚拟语气.是关于虚拟语气的,if he should come,please ...(let) me know.答案是填 If you should change your mind,do let me know.虚拟语气在这句话中是怎么体现 If you have any questions ,please put up your ( ). please put up your hands if you have any question------- If you have any question _____(ask),please hand up. 虚拟语气should have If you have any trouble ,please call me If you have any problem 虚拟语气中 用any 而不用some problem不加s,proble you would laugh if any one ...下面这句话是虚拟语气吗? what __you do if you ___ up 为什么不用虚拟语气? You will tell him that he should have studied此句有虚拟语气吗?为什么 If it should snow tomorrow,they couldn’t go out.这是虚拟语气吗?为什么?