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

Example Input: Humans host _ species of louse, the head louse , the body louse and the pubic louse .
Example Output: three

Example Input: Black women giving birth have a four to _ higher rate of mortality than white women do.
Example Output: one

Example Input: Ordinary tin is composed of _ stable isotopes.
Example Output:
nine