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: Neutrinos are particles with almost ____ mass and no electric charge.\Question: Choose the right answer from options given a) no b) two c) zero d) five
Example Output: a

Example Input: Redwoods reproduce ____ ways.\Question: Choose the right answer from options given a) zero b) two c) six d) nine
Example Output: b

Example Input: Some helicopters can have as many as ____ main rotor blades, and up to five tail rotor blades.\Question: Choose the right answer from options given a) six b) ten c) zero d) three
Example Output:
a