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 taxonomists classify only ____ species though.\Question: Choose the right answer from options given a) one b) six c) two d) three

A: c
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Q: Prairie dogs bear four or ____ young per litter.\Question: Choose the right answer from options given a) five b) eight c) two d) zero

A: a
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Q: Photons have momentum but ____ mass or electrical charge.\Question: Choose the right answer from options given a) zero b) no c) nine d) six

A:
b
****