How to quit a potential paper with my Master's supervisor when I am already doing the PhD somewhere else? For 1 year and half I did my master thesis in one laboratory, where although I learned a lot, it was mostly alone, having very reduced supervision and not having a project parallel to any of the PhD students. Finally by the time I delivered my thesis I learnt that I got accepted with a internship in a international institute (application that I did all by myself). My master supervisors were not happy as they wanted me to keep going with experiments to publish a paper. I did what I could before I left for the internship, even taught a new master students with the techniques I implemented. Also I transformed my thesis as much as possible in an article, still requiring just a few more experiments.  Now, one year and half later, having I already done 2 internships and started a very good PhD position in another country and scientific area, they still nag me with questions about the article. They did not contribute with any more experiments for the article and only one of the author corrected once the manuscript, only actually correcting the grammar and formatting. At this point I quitted  the article but clearly they still did not. I am indecisive if I should:
a) just stop replying, 
b) sent an email explaining that I want to focus on my PhD now and so I have no longer interest in the article
c) if I send the raw data and tell them to do whatever they want as long as I have the name somewhere and I can read one of the last versions.

The problem with c) is that although is the most "polite", I know they will keep nagging me and I will have a lot of work to prepare all the raw data (which include tons of images) to send them and most probably they will never actually publish it. With the other hypothesis the issue is that I do not want to have bad professional relationships. It is also important to refer that my thesis was presented in a poster in an international conference so it will not really bring much more scientific knowledge to publish it.
I would choose b) if I don't have much time to spare.

Work on every paper incurs an opportunity cost. Time spent at one place cannot be spent at another. If you have many exciting projects that need the time that you cannot afford to spend elsewhere, b) is what I would perceive to be the best option.

If however I have lots of time to spare, and no other project to work on, I would pick c). A publication increase is always a good thing in this case.