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: Humans normally produce only ____ sets of teeth.\Question: Choose the right answer from options given a) nine b) eight c) two d) three
Example Output: c

Example Input: Avian kidneys have ____ kinds of nephrons.\Question: Choose the right answer from options given a) four b) eight c) no d) two
Example Output: d

Example Input: Plants grow two to ____ feet tall.\Question: Choose the right answer from options given a) eight b) six c) three d) zero
Example Output:
c