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: Avian kidneys have ____ kinds of nephrons.\Question: Choose the right answer from options given a) four b) eight c) no d) two
Example Output: d

Example Input: Nightmares happen frequently in childhood, especially between the ages of ____ and six.\Question: Choose the right answer from options given a) three b) eight c) no d) ten
Example Output: a

Example Input: Children ages ____ to three years are the most common victims of poisoning.\Question: Choose the right answer from options given a) seven b) eight c) one d) four
Example Output:
c