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: Some snails can pull over ____ times their own body-weight.\Question: Choose the right answer from options given a) nine b) six c) five d) three
Example Output: d

Example Input: Facial features are smooth and very ____ dimensional.\Question: Choose the right answer from options given a) zero b) four c) ten d) three
Example Output: d

Example Input: Common iron is a mixture of ____ isotopes.\Question: Choose the right answer from options given a) one b) four c) three d) eight
Example Output:
b