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: Tilt consists of ____ small surface vents.\Question: Choose the right answer from options given a) zero b) three c) seven d) no
Example Output: b

Example Input: Cows breed at ____ years, bulls at four.\Question: Choose the right answer from options given a) two b) three c) seven d) one
Example Output: b

Example Input: Smoking is responsible for an estimated ____ in five U.S. deaths.\Question: Choose the right answer from options given a) five b) three c) one d) four
Example Output:
c