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

[EX Q]: Water is able to diffuse freely between the _ cells.
[EX A]: two

[EX Q]: Tin exists in _ allotropic forms.
[EX A]: three

[EX Q]: Cells become specialized, forming the _ germ layers found in all vertebrates.
[EX A]:
three