게 그러다

how can that be; be like that

그러다 is a stand-in verb — it replaces whatever was just said, like English 'do that, be like that'. With 어떻게 in front it becomes disbelief, which is what four of these lines are: 어떻게 그러지? 'how does that even happen?', 어떻게 그럴 수가 있냐! 'how could they do that!'. With other manner words it points back at a described state: 연장되게 그러면 'if it were extended like that'.

Register: casual, exclamatory