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]: 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
[EX A]: c

[EX Q]: Dunes are of ____ types - linear and parabolic.\Question: Choose the right answer from options given a) three b) four c) ten d) two
[EX A]: d

[EX Q]: Natural gas ranks number ____ in energy use, right after petroleum and coal.\Question: Choose the right answer from options given a) no b) three c) two d) nine
[EX A]:
b