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.

[Q]: Some people routinely sleep only ____ hours a night but feel fine during the day.
[A]: four


[Q]: Plants produce seed at ____ years of age.
[A]: eight


[Q]: Humans make ____ major forms of interferon.
[A]:
three