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

[EX Q]: Boolean operations is a method of combining _ meshes together.
[EX A]: two

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

[EX Q]: All cells act as sources, but most cells just propagate sound because they have _ amplitude.
[EX A]:
zero