题目内容：

1 （）,it immediately ran away.
a.Observing her b.On being oberved c.Having been oberved d.On her being oberverd
2 The experts were now fully convinced that the animal ( ) a puma.
a.must be b.should have been c.can only be d.could only have been

优质解答

1.B On ...和 when ...,意思都一样,“当……的时候”.On being observed也可以写作On the time when it is being observed 句意：一被人看到,美洲狮就跑掉了.2.D 情态动词表达推测的语意概念时,对于过去事实推测一定...