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: Elephants give birth to one calf every ____ to nine years on average.\Question: Choose the right answer from options given a) no b) four c) three d) seven
Example Output: b

Example Input: Triclinic system has ____ axes all of different lengths and all inclined to each other.\Question: Choose the right answer from options given a) two b) nine c) seven d) three
Example Output:
d