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

[EX Q]: Ozone leaves _ by-products except pure oxygen.
[EX A]: no

[EX Q]: Most anoles are said to live between _ and eight years.
[EX A]: four

[EX Q]: Most people see the world through _ types of visual-receptor cells.
[EX A]:
four