had somebody done somethingformal if someone had done something 如果某人做了某事 Had we known about it earlier, we could have warned people of the danger. 假如早点知道这件事的话,我们就能提醒人们有危险了。
had somebody done something• Had we known they were going to build a road right there, we would never have bought the house.
→ had somebody done something at have1(2)