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

Example Input: Induction also operates early in development, even before the _ layered embryo forms.
Example Output: three

Example Input: Polymorphism occurs in all species and the mandibles bear _ teeth.
Example Output: four

Example Input: Borrelia causes _ types of relapsing fever.
Example Output:
two