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

Example Input: Metals often crystallize in a _ dimensional version of the hexagonal closest packed structure.
Example Output: three

Example Input: Pups are unable to swim or find food until seven to _ weeks old or until the ice melts .
Example Output: eight

Example Input: Pups remain in the den for about _ weeks, and are cared for by the entire pack.
Example Output:
six