I don't know _____to send e-mail.A.how B.what C.which D.who

I don't know _____to send e-mail.A.how B.what C.which D.who I’m ________an English party nest week(plan)I really don't know what _____to you (say) I don't know. “i don't know you know i don't know sorry,I don't know. i don`t know much I don't really know. 英语；I don't know I don't know miss I don't know him. I don't know now 翻译 i don't know So know,I don't I don't know her i don't know anything I don't know _____to do .A.how:B.what:C.when:D.where 可以选什么?请大家帮我辨析下哈, I know enough to know that I don't know i don't know what i