C = Christianity,
A = All other religions, non-religion religions, and so on.
The common answer is that C is of grace; while A is always based on works.
I say, C starts with where you differ, not what you don't know; While A starts with what you don't know.
Many Chinese Christians love the phrase "不知者无罪", which is invalid in the case of C. Simply put, for all have sinned.