THE PRESENT PERFECT TENSE 1.They haven’t made any decision yet 2.No one has signed this letter 3.Has anyone shown you the new machine? 4.No one has seen Peter since the day of the party 5.Mr.Snow hasn’t taught that course since 1975 6.The city attorney(luật sư) has discovered new evidence 7.They have set up an investigation to look into the tragedy 8.Have doctors treated many people for burns and shock Passive : S + have/ has been Vp2 (W/H) +has/have +S +been +Vp2?