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]: Fish kills can occur when oxygen is less than ____ ppm.
[A]: three


[Q]: Clovers occasionally have leaves with ____ leaves, instead of the usual three.
[A]: four


[Q]: Lichens come in ____ different forms.
[A]:
three