In this process, all questions raised in the notice of examination opinions are answered one by one in written form (note that the answers should be based on the contents of the Patent Law and its implementing rules, and there can be no excuses without legal basis). When necessary, the application documents shall be amended, but the scope of the amendment must comply with the provisions of Article 33 of the Patent Law.
Generally speaking, unless the patent is written by you, not by an agent, there is no defense fee. The defense is generally done by the agent, and there is generally no charge.