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

Example Input: Morocco has _ perennial rivers and many dams have been built with potential for power generation.
Example Output: four

Example Input: Sake contains _ preservatives or sulfites.
Example Output: no

Example Input: Puppy teeth begin to shed and be replaced by permanent adult teeth at about _ months of age.
Example Output:
four