since when do you guys know each other为什么不用过去式

since when do you guys know each other为什么不用过去式 Since when have you known each other --Do you know when it was that they got to know each other - We__(know) each other since our boyhood what do you say when you meet each other? Do you two know each other?的意思 ___,do you know each other?For two weeks." when did you do that 中do 为什么用原形不用过去式? Do you know when the plane takes off?为什么不用将来时when the plane do you realize that we have not seen each other since the ni Jack and Susan______(know)each other since they were childre --Since when ________ each other --Oh I can't remember.