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: Cigarette smokers are ____ times more likely to die of lung cancer than nonsmokers.\Question: Choose the right answer from options given a) ten b) six c) four d) nine
Example Output: a

Example Input: Manatees swim two to ____ miles per hour.\Question: Choose the right answer from options given a) no b) six c) five d) zero
Example Output: b

Example Input: Barbershop harmony is a style of unaccompanied singing with ____ voices harmonizing to the melody.\Question: Choose the right answer from options given a) two b) eight c) four d) three
Example Output:
d