That smart girl studied a lot, so she ***(do) well on the test.
That smart girl studied a lot, so she must have done well on the test.
A: Who broke the big vase in the back office? B: It ***(be) Leo - he's very clumsy. But I'm not sure.
A: Who broke the big vase in the back office? B: It (might/may) have been Leo - he's very clumsy. But I'm not sure.
Scientists claim a giant asteroid hit the Earth in the Gulf of Mexico 65 million years ago and that ***(cause) the extinction of the big dinosaurs.
Scientists claim a giant asteroid hit the Earth in the Gulf of Mexico 65 million years ago and that must have caused the extinction of the big dinosaurs.