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

[Q]: Telescopes come in _ basic types - refractors and reflectors.
[A]: two


[Q]: Every muscle is made up of _ types of fibers.
[A]: two


[Q]: Hatchlings fall into _ main categories, nidicolous and nidifugous.
[A]:
two