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: Heat pumps give off ____ fumes or harmful products of combustion.\Question: Choose the right answer from options given a) four b) zero c) six d) no
Example Output: d

Example Input: Granite occurs in ____ separate masses.\Question: Choose the right answer from options given a) two b) eight c) nine d) no
Example Output: a

Example Input: Glycolysis is a determined sequence of ____ enzyme -catalyzed reactions.\Question: Choose the right answer from options given a) three b) two c) no d) ten
Example Output:
d