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: Sound waves travel through the air in a similar manner, but in all ____ dimensions.\Question: Choose the right answer from options given a) three b) five c) nine d) one
Example Output: a

Example Input: Today there are ____ UK hospitals doing heart transplants.\Question: Choose the right answer from options given a) three b) five c) six d) nine
Example Output: d

Example Input: Bacteria come in ____ forms - anaerobic and aerobic.\Question: Choose the right answer from options given a) two b) eight c) no d) six
Example Output:
a