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: Most bacteria have one or ____ circular chromosomes.\Question: Choose the right answer from options given a) ten b) eight c) six d) two
Example Output: d

Example Input: Some armored scales have ____ generations per year.\Question: Choose the right answer from options given a) four b) two c) no d) seven
Example Output:
a