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').

[EX Q]: 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
[EX A]: a

[EX Q]: Astronauts sleep only ____ hours each night, on average.\Question: Choose the right answer from options given a) six b) one c) four d) seven
[EX A]: a

[EX Q]: Flytraps spin when ____ creatures can be infected.\Question: Choose the right answer from options given a) six b) ten c) zero d) no
[EX A]:
d