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: Oranges signify good health, and the number ____ sounds like the word for prosperity .\Question: Choose the right answer from options given a) six b) four c) five d) eight
Example Output: d

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: Perennial grass takes three to ____ years before it is mature enough to produce adequate seed.\Question: Choose the right answer from options given a) five b) seven c) six d) four
Example Output:
a