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: Natural ytterbium is a mixture of ____ stable isotopes, with seven other unstable isotopes known.

Answer: seven


Question: Some nurseries only take children aged ____ years and over.

Answer: two


Question: Acorns mature in ____ years.

Answer:
two