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: Woodchucks produce about ____ young and virtually all females breed annually.\Question: Choose the right answer from options given a) ten b) four c) no d) six
Example Output: b

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: Mammals have ____ types of cartilage.\Question: Choose the right answer from options given a) ten b) eight c) zero d) three
Example Output:
d