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: Sexual maturity is reached at about ____ years of age.\Question: Choose the right answer from options given a) five b) ten c) no d) two
Example Output: d

Example Input: Onions are of ____ general types.\Question: Choose the right answer from options given a) seven b) two c) one d) zero
Example Output:
b