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]: Photosynthesis occurs in ____ phases.\Question: Choose the right answer from options given a) four b) two c) nine d) five
[EX A]: b

[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]: Bilaterian animals differ from the Cnidaria in ____ fundamental ways.\Question: Choose the right answer from options given a) no b) three c) five d) eight
[EX A]:
b