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: Mammals have only ____ sets of teeth.\Question: Choose the right answer from options given a) six b) five c) seven d) two
Example Output: d

Example Input: Cats have ____ lives.\Question: Choose the right answer from options given a) five b) one c) two d) nine
Example Output: d

Example Input: Plants produce seed at ____ years of age.\Question: Choose the right answer from options given a) one b) eight c) five d) nine
Example Output:
b