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

[Q]: Binary distillation separates _ chemicals.
[A]: two


[Q]: Bull sharks are a 'requiem' species, reaching up to _ feet in length.
[A]: ten


[Q]: Most ecosystems have only _ trophic levels, and the top carnivores are very rare.
[A]:
four