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: Meteorologists rely mainly on ____ types of satellites.\Question: Choose the right answer from options given a) four b) two c) ten d) three
Example Output: b

Example Input: Electrolytic capacitors have a useful life of about ____ years.\Question: Choose the right answer from options given a) ten b) eight c) zero d) seven
Example Output: a

Example Input: Insects go through either ____ or four stages.\Question: Choose the right answer from options given a) four b) six c) zero d) three
Example Output:
d