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: Ozone is a molecule containing ____ oxygen atoms.\Question: Choose the right answer from options given a) one b) nine c) no d) three

A: d
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Q: Elephants give birth to one calf every ____ to nine years on average.\Question: Choose the right answer from options given a) no b) four c) three d) seven

A: b
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Q: Lenses have ____ main shapes .\Question: Choose the right answer from options given a) one b) three c) five d) six

A:
b
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