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

[EX Q]: Cleavage is imperfect in _ directions, prismatically.
[EX A]: two

[EX Q]: Canids only have _ toes.
[EX A]: four

[EX Q]: Univalves have one shell, and bivalves have _ shells.
[EX A]:
two