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: Wolverines reproduce every ____ or three years.\Question: Choose the right answer from options given a) two b) three c) one d) four
Example Output: a

Example Input: Potential energy is divided into ____ different types of energy.\Question: Choose the right answer from options given a) eight b) three c) zero d) two
Example Output: b

Example Input: Galaxies exist in ____ basic forms, with variations.\Question: Choose the right answer from options given a) seven b) two c) zero d) ten
Example Output:
b