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

[EX Q]: Aquatic adults have prominent red reathery gills, are large, and have _ toes on each foot.
[EX A]: four

[EX Q]: Pelycosaurs are a paraphyletic group of _ primitive families of synapsids.
[EX A]: six

[EX Q]: Frogs require from four to _ years to reach maturity.
[EX A]:
eight