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

[EX Q]: Pelagic division is divided into neritic and _ levels of pelagic provinces.
[EX A]: three

[EX Q]: Psychiatrists categorize symptoms into _ categories.
[EX A]: three

[EX Q]: Some molecules consist of _ atoms of the same element.
[EX A]:
two