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: Marriage is the legal union of ____ people.\Question: Choose the right answer from options given a) one b) no c) five d) two
Example Output: d

Example Input: Widowed men are ____ times as likely to be murdered.\Question: Choose the right answer from options given a) two b) four c) three d) no
Example Output: b

Example Input: Chloroplasts are larger than mitochondria, and are surrounded by ____ specialized membranes.\Question: Choose the right answer from options given a) four b) six c) zero d) three
Example Output:
d