The triangle problem I am planning to publish a research paper based on my internship and don't know in what order I must include the author names or whom to include in the paper. Professor A was the primary reason for me to join the internship, while Professor B is just my guide who initially didn't approve of me doing the internship but later started to motivate me. Intern C had helped me a lot to complete the project whose help has been crucial to me. All 3 actually told me to publish the paper and Professor B guided me with the websites and reviewing my papers. But Professor A also initially guided me with the paper. How am I to rank these people for the authors in the paper?

Prof A- Initial guidance with some ideas to improve my presentation and strong support without which I wouldn't even have taken up the internship

Prof B- Support only at the later stage to publish paper and reviewed the papers

Intern C-Can't imagine myself to have completed the project (based on which the research paper is constructed) without her.

Thanks in advance!
You wrote the paper, did the main research, hence your name should go first.

The interns contribution is crucial to this paper, she/he helped a lot, but was not so much involved in the writing process? Name her/him second.

Professor B help a lot with constructing the paper, writing, rewriting, reviewing, etc. Put her/him second to last. Indicate her/him as correspondence author, too.

Since professor A is the main initiator, I assume that the research you did is within his field. He might therefore be also the main correspondence author. He will probably also handle submission and other formalities with the journal. Put him last.   

Final Order:
You, Intern C, Professor B,* and Professor A.*

In any way, the person who will handle the submission process, will probably also review this. Don't think too much about the order. In many cases it does not really matter, and most professors do not care too much about this, as they are usually named as correspondence authors anyway.