why的问句为什么有时用why can‘I do sth..有时又用Why we should do sth.到底助动词

why not do sth why not +do sth 用"why not do sth"造句 why not do sth全句是 why shall we not do sth why not do sth ?的用法 why not doing sth还是why not do sth还是why not to do sth why not doing sth和 why not do sth的区别 why not to do sth对吗?waiting why not do sth sb放哪? why not do sth?怎么回答 why dont sb.do sth.同义句 简单英语造句1、shall we do (sth.2、let's do (sth.).3、why not do (sth