an "A" represents the class of --comparatively speaking-- the best-answer tests. here is one example of that class:
p. 1, see that in question 5- "karma," she goes in detail to explain the concept. or in question 7- "ahimsa" how she develops her idea. this student doesn't answer a question just with a one-liner, she actually explains what she knows.
p.2, see for instance in the question 10- "gunas," how the student specifies each one and goes further to explain each one. she doesn't miss one.