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

[Q]: Stroke is our nation's number _ killer, and a leading cause of disability for older adults.
[A]: three

[Q]: Seasons occur because of _ factors working together.
[A]: two

[Q]: Golden jackals live eight to _ years in the wild and up to sixteen in captivity.
[A]:
nine