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: Some sources claim there are more like ____ million vertebrate animals in zoos.\Question: Choose the right answer from options given a) six b) five c) one d) three

A: b
****
Q: Islamic practice is based on what are called the ____ pillars of faith.\Question: Choose the right answer from options given a) eight b) one c) five d) four

A: c
****
Q: Ozone is a naturally occurring molecule containing ____ atoms of oxygen.\Question: Choose the right answer from options given a) three b) five c) nine d) eight

A:
a
****