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').

ATMs are expensive machines with an average useful life of ____ to fifteen years.\Question: Choose the right answer from options given a) nine b) eight c) ten d) two
c

Astronomical observations suggest ____ or close to zero space-time curvature.\Question: Choose the right answer from options given a) six b) zero c) ten d) seven
b

Wood burns in ____ stages.\Question: Choose the right answer from options given a) two b) three c) five d) eight

b