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: 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: Most birds have ____ toes, three that face forward and one rearward.\Question: Choose the right answer from options given a) two b) ten c) nine d) four
Example Output: d

Example Input: Abdominoplasty usually takes ____ or four hours, depending on the extent of work required.\Question: Choose the right answer from options given a) five b) six c) ten d) three
Example Output:
d