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').

[Q]: Infants can tell their mothers from other mothers in ____ days.\Question: Choose the right answer from options given a) no b) zero c) five d) three
[A]: d


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


[Q]: Acquired immunity is of ____ types, active and passive.\Question: Choose the right answer from options given a) seven b) two c) nine d) one
[A]:
b