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]: 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]: Some sources claim there are more like ____ million vertebrate animals in zoos.\Question: Choose the right answer from options given a) six b) five c) one d) three
[EX A]: b

[EX Q]: Calves suckle for ____ years then eat solid food.\Question: Choose the right answer from options given a) four b) two c) nine d) six
[EX A]:
b