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

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

[EX Q]: Crustaceans have _ major body parts .
[EX A]: three

[EX Q]: Pyrimidines contain one ring and purines contain _ rings.
[EX A]:
two