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]: Heme is made of ____ pyrrole groups united to form a porphyrin ring.\Question: Choose the right answer from options given a) five b) four c) eight d) six
[A]: b


[Q]: National forests have regulations that restrict ____ wheeler use to established roads.\Question: Choose the right answer from options given a) no b) four c) six d) nine
[A]: b


[Q]: Ospreys reach sexual maturity between ____ and five years of age.\Question: Choose the right answer from options given a) three b) four c) two d) eight
[A]:
a