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: Color codes are ____ digit combinations of letters and numbers that correspond to a specific color.\Question: Choose the right answer from options given a) six b) eight c) seven d) one
Example Output: a

Example Input: Humans normally produce only ____ sets of teeth.\Question: Choose the right answer from options given a) nine b) eight c) two d) three
Example Output: c

Example Input: Ozone is comprised of ____ oxygen molecules which acts as an oxidizer and bacterial disinfectant.\Question: Choose the right answer from options given a) five b) nine c) three d) zero
Example Output:
c