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

[EX Q]: Retinoic acid regulates oral epithelial differentiation by _ mechanisms.
[EX A]: two

[EX Q]: Meerkats can have one to seven babies at _ time.
[EX A]: one

[EX Q]: Goats are _ legged animals.
[EX A]:
four