【语法题,Isupposeyouarenotserious,________?A.doIB.don'tIC.areyouD.aren'tyou这个什么情况下用don't________,Ishouldaskthemsomequestions.A.ShouldtheycometousB.IftheycometousC.WeretheycometousD.HadtheycometousS】

　　语法题,

　　Isupposeyouarenotserious,________?

　　A.doIB.don'tIC.areyouD.aren'tyou

　　这个什么情况下用don't

　　________,Ishouldaskthemsomequestions.

　　A.ShouldtheycometousB.Iftheycometous

　　C.WeretheycometousD.Hadtheycometous

　　Somecitieshavepassedlawsthatallowcoalandoil_____onlyiftheirsulfurcontentislow.

　　A.burningB.toburnC.beingburnedD.tebeburned

　　allowsbtodo和allowsbdong都可以的吧

　　为什么不选其他的,请大家给我个详尽的解释哈,