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: Astronauts sleep only ____ hours each night, on average.\Question: Choose the right answer from options given a) six b) one c) four d) seven
Example Output: a

Example Input: Tardigrades are microscopic, water-dwelling, segmented animals with ____ legs.\Question: Choose the right answer from options given a) eight b) nine c) one d) seven
Example Output: a

Example Input: Olympic athletes tour the country every ____ years after the Olympics.\Question: Choose the right answer from options given a) ten b) four c) two d) eight
Example Output:
b