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

[EX Q]: Flytraps spin when _ creatures can be infected.
[EX A]: no

[EX Q]: Falcons are roughly divisible into three or _ groups.
[EX A]: four

[EX Q]: Natural oxygen is a mixture of _ isotopes.
[EX A]:
three