【Youshouldsay"Thankyou"whensomeonepassesyouthesaltonthetable,whensomeonewalkingbeforeyoukeepthedooropenforyou,whensomeonesaysyouhavedoneyourworkwell,youhaveboughtanicething,oryourcityisverybeautiful.（1~2）1.】

　　Youshouldsay"Thankyou"whensomeonepassesyouthesaltonthetable,whensomeonewalkingbefore

　　youkeepthedooropenforyou,whensomeonesaysyouhavedoneyourworkwell,youhaveboughtanicething,oryourcityisverybeautiful.（1~2）

　　1.为什么whensomeonesays中用says而不用saying,况且上文也有whensomeonewalkingbeforeyoukeepthedooropenforyou

　　（难道是句中的before可是都是介词后的动词加ing呀）

　　2.为什么whensomeonewalkingbeforeyoukeepthedooropenforyou中要用keep而不用keeping,句子中不是有before吗

　　3.HaveyourparentsflowntoShanghai?

　　Yes.Theywenttheretoseethefashionshow.

　　问句中为什么用现在完成时,答句中用过去时.