In this task, find the most appropriate number to replace the blank (indicated with _ ) and express it in words.

Q: Diarrhea is an illness that kills _ and one-half million children per year.

A: three
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Q: Retinoic acid regulates oral epithelial differentiation by _ mechanisms.

A: two
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Q: Smokers die an average of _ to eight years earlier than nonsmokers.

A:
six
****