I have told them with absolute certainty there'll be no change of policy.我已经十分肯定地告诉他们，政策不会变。I thought he'd been drinking, though I wasn't completely sure.我觉得他一直在喝酒，不过不是十分肯定。I think his name is John, although I'm not completely sure about that.我认为他名叫约翰，但我并不十分肯定。