Inversion当中的取代if的虚拟语句中,如何分were,had和should的用法
例如,1.Hadthebooksbeencheaper,Iwouldboughtthemall.
2.Weretheministertofailtogetthenecessarysupport,hewouldbeforcedtocallasnapelection.
3.Shouldyouneedanyfurtherassistance,donothesitatetocontactus.
这3个的用法如何不同呢?