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: Today there are ____ federal states, each based on cultural affiliations.\Question: Choose the right answer from options given a) one b) nine c) seven d) zero
Example Output: b

Example Input: All mass spectrometers consist of ____ distinct regions.\Question: Choose the right answer from options given a) three b) one c) two d) zero
Example Output: a

Example Input: Antlers take about ____ months to grow.\Question: Choose the right answer from options given a) four b) ten c) one d) two
Example Output:
a