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: Most bioluminescence is blue for ____ reasons.\Question: Choose the right answer from options given a) seven b) two c) four d) zero
Example Output: b

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: Diarrhoea kills ____ million children under five every year.\Question: Choose the right answer from options given a) zero b) three c) five d) six
Example Output:
b