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: Natural chlorine contains ____ isotopes.\Question: Choose the right answer from options given a) two b) six c) eight d) seven

A: a
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Q: Dogs are pack animals, and ____ dogs is the minimum number for proper socialization.\Question: Choose the right answer from options given a) four b) five c) no d) zero

A: b
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Q: Gregorian chants are divided into ____ types based on the number of notes sung to each syllable .\Question: Choose the right answer from options given a) four b) six c) no d) three

A:
d
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