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: Astronomers fall in ____ classes - professionals and amateurs.\Question: Choose the right answer from options given a) two b) four c) six d) zero
Example Output: a

Example Input: Embrasures have ____ functions.\Question: Choose the right answer from options given a) three b) seven c) zero d) nine
Example Output: a

Example Input: Children learn more during the first ____ years of life than at any other time.\Question: Choose the right answer from options given a) one b) five c) no d) six
Example Output:
b