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 ____ basic classifications of sausage.\Question: Choose the right answer from options given a) five b) four c) six d) one
Example Output: a

Example Input: Sexual reproduction involves ____ individual organisms.\Question: Choose the right answer from options given a) six b) no c) two d) nine
Example Output: c

Example Input: Trees are keys to ecological land use for ____ reasons.\Question: Choose the right answer from options given a) two b) three c) six d) seven
Example Output:
b