The title is a bit long but let me explain. I am a final year undergraduate student and am currently applying for a PhD in my field. All the universities I am applying to require three letters of recommendation (LoR). My supervisor for my Bachelors Thesis is writing me one letter and a Professor with whom I did a summer internship is writing me the other, so in total I have two research supervisors writing me a letter each. Now for the third LoR I am a bit confused about whom to ask. Here are my options:
- Professor A: I got an average grade (my grade was 7, and 10 is the highest you can get) in his class but I have had a lot of interactions with him since that class. Basically when I was looking for research groups to apply to (in his field), he guided me a lot and recommended many groups and put me in touch with one of his colleagues. I also approached him when I wanted to learn some advanced topics and he gave me some papers to read, and we will be having discussions on them.
- Professor B: He is the faculty advisor of my class (as in he signs some of our official documents and things like that). I have done two courses with him, one of which I got a 9 grade (few people got a 9 or a 10 because the course was tough) and an 8 in the other. The first course had a project and my team was adjudged to have the best presentation in that class. I have also had some interactions with him but they were mostly unrelated to course material. He also did help me out a bit with figuring out how to apply to grad schools.
- Professor C: I did very well in her course (10) and also did a course project with her. But that course was around two years ago and I don't know if she remembers me because I haven't interacted with her since then.
I was initially inclined to ask Professor A since I have a good rapport with him but I don't know if I should ask him because I hadn't done very well in his course, so I don't know if he would write me a strong LoR.
What should I do?