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: Water is the only substance on earth found naturally in ____ forms - solid, liquid, and gas.

Answer: three


Question: Plants generally live ____ years but sometimes longer.

Answer: two


Question: Oral tolerance is induced by at least ____ mechanisms.

Answer:
two