Help choosing my recommender: weaker letter from faculty with PhD, or strong letter from non-PhD industry boss? I know none of the choices below are ideal, but I've exhausted my options.  I'm applying for PhD in mechanical engineering to US schools, some of which specifically stated letters must come from someone who is familiar with my academic work.  I would like advice on which person below might be the best choice, I need to pick one.
PERSON A

PhD/ mech engg professorial position (different subdiscipline than my interest), might be difficult to contact due to pandemic
I took a class.  Grade is pretty good and above average, but not stellar.  I think the letter will just be &quot;took a class&quot; letter.
Was adviser for an engineering undergraduate competition (in unrelated mech engg subdiscipline) that didn't reach fruition (we had to back out at the final stage of the competition, lasted several months).  It didn't go that well, so I don't think I want to remind him about it.

PERSON B

BS mechanical engineering, BS applied physics, masters in mechanical engineering in decent school in US
Taught in my university/department for a brief period, a long time ago
supervises me in my work (1 year).  I have 3 main roles:  two of which are normal engineering roles involving design/analysis, one of which is industry heavy R&amp;D (that's largely confidential and won't have publications).  But I think he will be able to write well of my ability to work independently in R&amp;D, and will be able to speak well of my analytical/critical thinking skills since my other roles involve problem solving
right from the job interview, I already said clearly I don't plan to stay here and my dream is to work in research and get a PhD.  So he will be able to speak of how much I want to get into PhD

PERSON C

Non PhD/ ex-faculty.  No longer affiliated with university, can't use university letterhead.
Stellar grades in class, in semi related field (he taught mechanisms, I'm interested in dynamics)
I've had conversations with him in the past, asking for advice about graduate study, so he knows me a little more than someone who just attended class.

The deadlines are on Dec. 1, and I still don't have recommendations.  I've been emailing other more &quot;ideal&quot; profs since last month, but I won't be able to get letters from them.  One of them, I did a workshop under him in my chosen field, got the highest possible grade in his class, and also worked with him in engineering competitions that went okay, but he rejected my request.  The other one, is the professor I did laboratory assistantship under, who also won't be able to write my letter and I can't contact anymore.  So the choices I stated above, are my only choices.
Person B seem the best person to assess your at least &quot;academic related&quot; work. That said, in my (non-US) experience reference letters very, very rarely if at all play a major role when making decisions whom to admit, as long as they are &quot;kind of OKish&quot; and the writer has at least some qualification to write them. So you shouldn't be worried of making an all too big mistake here; chances are that your success will not rely on your recommender choice. I'd probably avoid Person C but I don't think Person A will do you much harm. If I were Person A, I'd have a look at your overall results, and mention positively if they are better than what you did in my class (which apparently isn't exactly bad either).