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: Female elephants have babies about ____ years apart, and they have only one each time.\Question: Choose the right answer from options given a) eight b) one c) zero d) three
Example Output: d

Example Input: Babies are breast-fed until about ____ years of age.\Question: Choose the right answer from options given a) four b) nine c) eight d) two
Example Output: d

Example Input: Most burn injuries occur to children less than ____ years of age.\Question: Choose the right answer from options given a) one b) three c) eight d) six
Example Output:
b