Given a sentence, fill out the missing word with a 'no' or a number (between zero and ten). You should write the numbers with english alphabet, like: four instead of 4.
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Question: Blood donors can give blood every ____ weeks, or six times a year.

Answer: eight


Question: Cytochrome oxidase consists of two cytochromes and ____ copper atoms.

Answer: two


Question: Enzyme activity is controlled at ____ different levels.

Answer:
two