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]: National immunization vaccinates all children under ____ against polio.\Question: Choose the right answer from options given a) zero b) four c) ten d) five
[EX A]: b

[EX Q]: Respiratory therapists complete ____ to four years of education.\Question: Choose the right answer from options given a) one b) nine c) zero d) two
[EX A]: d

[EX Q]: Bowhead whales are slow swimmers and usually travel alone or in small herds of up to ____ animals.\Question: Choose the right answer from options given a) nine b) six c) eight d) ten
[EX A]:
b