Given a sentence with a missing word, pick the answer option that best fills out the missing word in the sentence. Indicate each answer with its index ('a', 'b', 'c', 'd').

Example Input: Metals often crystallize in a ____ dimensional version of the hexagonal closest packed structure.\Question: Choose the right answer from options given a) one b) seven c) three d) eight
Example Output: c

Example Input: Bloody diarrhea lasts for two to ____ days.\Question: Choose the right answer from options given a) nine b) five c) three d) no
Example Output: b

Example Input: Many mammals have hooves that are cloven with ____ parts.\Question: Choose the right answer from options given a) two b) six c) one d) nine
Example Output:
a