B = honorable effort. Fullfilled the assignment, in (1) demonstrating some relation to the course's themes and readings,(2) successfully demonstrating some technique (it worked), (3) giving some response to the question "why is it interesing?" in some terms, cultural / historical / symbolic, artistic / experiential, or technical.
A = exceptional effort. B work plus something extra in some dimension that contitutes extra diligent research or an imaginative innovation.
C = significantly lacking from B work.
with nuances and allowances