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: Reverse osmosis uses three to ____ gallons of water to produce one gallon of drinking water.\Question: Choose the right answer from options given a) six b) eight c) five d) ten
Example Output: d

Example Input: Pairs encodes all sets of objects with ____ components.\Question: Choose the right answer from options given a) ten b) five c) two d) no
Example Output: c

Example Input: Female dugongs give birth to just ____ calf about once every five years.\Question: Choose the right answer from options given a) four b) three c) nine d) one
Example Output:
d