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: Toenails are similar , except that they grow ____ times slower and are on the toes .\Question: Choose the right answer from options given a) two b) eight c) six d) four
Example Output: d

Example Input: Carbon forms ____ bonds.\Question: Choose the right answer from options given a) five b) four c) two d) three
Example Output: b

Example Input: Cometary orbits come in ____ classes.\Question: Choose the right answer from options given a) one b) eight c) two d) zero
Example Output:
c