Answer:
fac·ul·ta·tive
/ˈfakəlˌtādiv/
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adjective
occurring optionally in response to circumstances rather than by nature.
"the difference between facultative skin pigmentation and constitutive pigmentation is a function of overall sun exposure"
BIOLOGY
capable of but not restricted to a particular function or mode of life.
"a facultative parasite"
Explanation:
