What Is the Difference Between an Obligate and a Facultative

Multiple Choice

What is the difference between an obligate and a facultative symbiosis?

A) Obligate symbiosis occurs earlier in evolution than facultative symbiosis.
B) In an obligate symbiosis, the partners are totally dependent upon one another, which is not the case for a facultative symbiosis.
C) In an obligate symbiosis, one partner is internalized, whereas this is not the case in a facultative symbiosis.
D) A facultative symbiosis always involves degeneracy, which is not true for an obligate symbiosis.