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

[EX Q]: Reverse osmosis uses three to ten gallons of water to produce _ gallon of drinking water.
[EX A]: one

[EX Q]: Anemone has _ vents.
[EX A]: two

[EX Q]: Wheat is an old combination of _ different species of grass.
[EX A]:
three