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: Astronomers fall in ____ classes - professionals and amateurs.\Question: Choose the right answer from options given a) two b) four c) six d) zero

A: a
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Q: Cows have four stomachs, and the first ____ yield merchantable tripe.\Question: Choose the right answer from options given a) two b) five c) zero d) three

A: d
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Q: Crude oil is recovered by drilling holes as deep as ____ miles into the earth's crust.\Question: Choose the right answer from options given a) four b) five c) ten d) nine

A:
b
****