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]: 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
[EX A]: b

[EX Q]: Cats have ____ sets of vocal cords.\Question: Choose the right answer from options given a) zero b) nine c) two d) three
[EX A]: c

[EX Q]: Some books claim abductions happen once every ____ years.\Question: Choose the right answer from options given a) two b) ten c) five d) nine
[EX A]:
c