Use the Information and Figure to Answer the Following Question

Multiple Choice

Use the information and figure to answer the following question.
The sea slug Pteraeolidia ianthina can harbor living dinoflagellates (photosynthetic protists) in its skin. These endosymbiotic dinoflagellates reproduce quickly enough to maintain their populations. Low populations do not affect the sea slugs very much, but high populations (> 5 × 10⁵ cells/mg of sea slug protein) can promote sea slug survival.

Percent of sea slug respiratory carbon demand provided by indwelling dinoflagellates.
According to the graph, during which season(s) of the year is the relationship between the sea slug and its dinoflagellates closest to being commensal?

A) winter
B) spring
C) summer
D) spring and summer