英语解释 Not to mention imaginary

the search proved difficult ,to mention imaginary ,为什么形容词dif not to mention等于 英语翻译not to mention less than 和not to mention区别 let alone not to mention 区别 not to mention 后面跟什么结构 Those things are gone, I do not want to mention not to mention going abroad为什么是ing let alone和not to mention有什么区别? Not to mention和let alone的区别 英语翻译"Learning would be exceedingly laborious,not to mention much less和not to mention有什么区别?