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

[Q]: Water has _ characteristics that are particularly important to lakes.
[A]: two


[Q]: Carbon dioxide extinguishes fire by physically attacking all _ points of the fire triangle.
[A]: three


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