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

[EX Q]: Zeolites have basically _ different structural variations.
[EX A]: three

[EX Q]: R is an average of the color rendering ability of _ or more specific colors.
[EX A]: eight

[EX Q]: Echocardiography demonstrates in clear, graphic fashion the _ cardiac chambers and four valves.
[EX A]:
four