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

Ex Input:
Scientists use a characteristic to classify animals into _ groups.

Ex Output:
two

Ex Input:
Dwarf trees are diminutive and shrub-like, reaching _ feet or so at maturity.

Ex Output:
four

Ex Input:
Natural gas ranks number _ in energy use, right after petroleum and coal.

Ex Output:
three