challenge: What is the meaning of 'exhaustivity' in linguistics when a speaker says 'Ava got an A' in response to the question 'Which students got an A?'
  
  A. Ava was the only student who did not get an A
  B. Ava did not get an A, but the speaker is unsure about other students
  C. Ava was among the students who got an A, but it does not rule out others getting an A
  D. Ava was the only student who got an A, and no other students got an A
  Answer: 