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

Input: Consider Input: Humans brains are about _ times bigger than in chimpanzees.

Output: three

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

Output: three

Input: Consider Input: Fleas are small wingless insects averaging two to _ millimeters.
Output: four