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

[EX Q]: Frozen grafts can have a shelf life of up to _ years.
[EX A]: five

[EX Q]: Pure water contains _ ions and is therefore a nonconductor .
[EX A]: no

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