A.: When the doctor cures Rivers wrist using some of his regeneration power.
I know it may sound strange to like this scene but I like for what it stands for, for what it represents. And it represents a lot if you think about it. For one hand you have River pretending not to be hurt to protect the feelings of the man she loves, for another you have the Doctor hurt about her pain and willing to abdicate some of his regeneration power to cure her. In my mind this scene is the best proof of love both of them give to each other. Both of them are giving so much, and protecting the one they love.