Answer
See explanation for a detailed answer.
Work Step by Step
a)The question "Are you a liar?" does not work because of the following:
The cannibal either lies or tells the truth
1) If he tells the truth, he will answer no.
2) If he lies, he will answer no.
Therefore, the explorer cannot know if he lies or tells the truth because the answer will be the same.
b) One of the questions which might work is "If I asked you if you are a liar what would you answer?"
1) If the cannibal is telling the truth, he will answer No.
2) If the cannibal lies, he will answer Yes.
