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: Natural tellurium consists of ____ isotopes.\Question: Choose the right answer from options given a) six b) seven c) eight d) one
Example Output: c

Example Input: Water softeners add sodium to drinking water in ____ ways.\Question: Choose the right answer from options given a) zero b) six c) two d) nine
Example Output: c

Example Input: Volume is the amount of ____ dimensional space an object occupies.\Question: Choose the right answer from options given a) zero b) seven c) three d) four
Example Output:
c