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]: Ants have six legs, and each leg has ____ joints.\Question: Choose the right answer from options given a) nine b) zero c) two d) three
[EX A]: d

[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]: White bison are extremely rare, historically appearing only once in every ____ million births.\Question: Choose the right answer from options given a) seven b) five c) nine d) ten
[EX A]:
b