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]: Today there are ____ federal states, each based on cultural affiliations.\Question: Choose the right answer from options given a) one b) nine c) seven d) zero
[EX A]: b

[EX Q]: Stable oxygen has eight protons and ____ neutrons.\Question: Choose the right answer from options given a) eight b) ten c) three d) zero
[EX A]: a

[EX Q]: Female elephants have babies about three years apart, and they have only ____ each time.\Question: Choose the right answer from options given a) one b) four c) five d) six
[EX A]:
a