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

Example Input: Premolars have one, two, and sometimes _ canals.
Example Output: three

Example Input: Every earmark consists of a symbol in _ positions.
Example Output: two

Example Input: Abdominoplasty usually takes three or _ hours, depending on the extent of work required.
Example Output:
four