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

[EX Q]: Vitamins are classified into _ groups.
[EX A]: two

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

[EX Q]: Parallel hybrids have _ discrete power systems, gas and electric.
[EX A]:
two