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: Ground squirrels breed once a year, averaging ____ to eight per litter.\Question: Choose the right answer from options given a) seven b) one c) six d) ten

A: a
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Q: Sexual reproduction involves ____ parents, one male and one female.\Question: Choose the right answer from options given a) zero b) two c) nine d) four

A: b
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Q: Budgerigars are probably easiest to sex when they reach maturity at ____ to seven months old.\Question: Choose the right answer from options given a) five b) six c) seven d) no

A:
b
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