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: Young children suffer from an average of six to ____ colds a year.\Question: Choose the right answer from options given a) ten b) eight c) two d) one
Example Output: b

Example Input: National forests have regulations that restrict ____ wheeler use to established roads.\Question: Choose the right answer from options given a) no b) four c) six d) nine
Example Output: b

Example Input: Rapid growth occurs for the first ____ years of life.\Question: Choose the right answer from options given a) eight b) ten c) three d) five
Example Output:
d