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: Elk retain their antlers for more than ____ months of the year.\Question: Choose the right answer from options given a) nine b) ten c) six d) seven
Example Output: c

Example Input: Euglenids have one or more often ____ flagella.\Question: Choose the right answer from options given a) seven b) four c) eight d) two
Example Output:
d