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

[EX Q]: Every drug has _ names, a chemical name, a brand name, and an official name.
[EX A]: three

[EX Q]: Older caterpillars have _ different color forms.
[EX A]: two

[EX Q]: Copper has _ naturally occurring isotopes.
[EX A]:
two