have/has been doing否定形式
是“They don't have been seeing each other these days.”
是“They haven't been seeing each other these days.”
Have you been learning English for ten years?
是 No,I have't.
还是 No,I don't.
是 It is necessary of us to help others when they are in trouble.
还是 It is necessary for us to help others when they are in trouble.