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: Evolution is dependent on ____ forces.\Question: Choose the right answer from options given a) no b) five c) two d) seven
Example Output: c

Example Input: Most birds have ____ toes, three that face forward and one rearward.\Question: Choose the right answer from options given a) two b) ten c) nine d) four
Example Output: d

Example Input: Ammonia is added ____ hours after the chlorine, in a process called chloramination .\Question: Choose the right answer from options given a) four b) eight c) one d) three
Example Output:
d