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]: 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]: Human malaria is caused by ____ species of Plasmodium . .\Question: Choose the right answer from options given a) six b) ten c) seven d) four
[EX A]: d

[EX Q]: Ferrets live roughly for about forty ____ most preferred toy or for sleeping.\Question: Choose the right answer from options given a) two b) five c) four d) six
[EX A]:
b