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: Voles are prolific breeders and can produce four to ____ litters a year.\Question: Choose the right answer from options given a) four b) two c) six d) three
Example Output: c

Example Input: Elephants have four molars, which are replaced ____ times, for a total of six sets in a lifetime.\Question: Choose the right answer from options given a) five b) no c) three d) one
Example Output: a

Example Input: Wing feathers are now ____ months old and continue to fade and wear.\Question: Choose the right answer from options given a) eight b) six c) ten d) zero
Example Output:
c