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: Brain death occurs in just four to ____ minutes unless the heart rhythm is restored.\Question: Choose the right answer from options given a) ten b) three c) six d) nine
Example Output: c

Example Input: Urea cycle requires the coordination of ____ different tissues.\Question: Choose the right answer from options given a) two b) four c) nine d) zero
Example Output: a

Example Input: TriMetal Irons Discover the benefits of ____ different metals.\Question: Choose the right answer from options given a) five b) seven c) no d) three
Example Output:
d