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: Whales are divided into ____ categories, based on their teeth.\Question: Choose the right answer from options given a) two b) four c) nine d) ten
Example Output: a

Example Input: Ammonia is among the ____ most abundantly produced chemicals in the world.\Question: Choose the right answer from options given a) five b) zero c) no d) eight
Example Output: a

Example Input: Dietary supplements are particularly important for older people for ____ reasons.\Question: Choose the right answer from options given a) three b) two c) eight d) seven
Example Output:
a