I have no idea what____while I was asleep.(happen)
老师说填 happened 为什么不用 was happening呢？
The boys played computer games happily,____all about their homework.(forget) 为什么是forgetting 呢？
1，因为他已经做过了，属于过去完成进行时`有过去时+ed
2，forgetting是forget的现在时，意思是忘记~，句子意思是：这个男孩玩电脑游戏很快乐，（但）他忘记做他的作业了。前面是过去完成时，后面是将来时，因为他还没有做作业，所以有ing型式。