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: Rock cavies become sexually mature when they are about one to ____ months old.\Question: Choose the right answer from options given a) one b) four c) three d) seven
Example Output: c

Example Input: Cleavage occurs typically in either one, two, three, four, or ____ directions.\Question: Choose the right answer from options given a) six b) three c) ten d) two
Example Output: a

Example Input: Respiratory changes associated with aging include ____ of the following.\Question: Choose the right answer from options given a) five b) zero c) three d) ten
Example Output:
c