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

[EX Q]: Retinoic acid regulates oral epithelial differentiation by _ mechanisms.
[EX A]: two

[EX Q]: Tetrachoric correlation is _ artificially dichotomous variables.
[EX A]: two

[EX Q]: Tetrads come in _ shapes.
[EX A]:
seven