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: Motor neurons are divided into ____ groups.\Question: Choose the right answer from options given a) two b) six c) seven d) eight
Example Output: a

Example Input: Mechanical stability comes from having fused quartz, in ____ gravity, cold.\Question: Choose the right answer from options given a) five b) zero c) six d) two
Example Output: b

Example Input: Object permanence is seen in children ____ to twelve months old.\Question: Choose the right answer from options given a) one b) eight c) six d) nine
Example Output:
b