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: Sea stars have ____ arms, or rays, connected to a small round body.\Question: Choose the right answer from options given a) five b) six c) seven d) no
Example Output: a

Example Input: Most aphthous ulcers heal in one to ____ weeks.\Question: Choose the right answer from options given a) two b) eight c) one d) seven
Example Output: a

Example Input: Some sharks can replace their front teeth every ____ weeks.\Question: Choose the right answer from options given a) two b) four c) nine d) seven
Example Output:
a