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]: Natural indium contains ____ isotopes.\Question: Choose the right answer from options given a) one b) eight c) two d) seven
[EX A]: c

[EX Q]: Copper is ____ times higher in dog liver than in human liver.\Question: Choose the right answer from options given a) three b) ten c) six d) one
[EX A]: b

[EX Q]: Most bacteria are ____ or two microns wide.\Question: Choose the right answer from options given a) two b) five c) ten d) one
[EX A]:
d