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: Cleavage is perfect in ____ directions, prismatic.\Question: Choose the right answer from options given a) two b) nine c) three d) seven
Example Output: a

Example Input: Food waste is transformed into soil-like humus in ____ to seven days.\Question: Choose the right answer from options given a) ten b) five c) zero d) three
Example Output: d

Example Input: Black rhinos have ____ horns, one longer than the other.\Question: Choose the right answer from options given a) no b) two c) seven d) five
Example Output:
b