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

[EX Q]: Terrorism is a problem which has troubled the international community for more than _ decades.
[EX A]: three

[EX Q]: Phosphates are made of _ phosphorus atom surrounded by four oxygen atoms.
[EX A]: one

[EX Q]: Periodontal disease is the most common condition in the ferret older than _ years.
[EX A]:
six