Which of the following is a compound-complex sentence?

a.
my mother and my sister are on opposite sides of the controversy, but i have chosen to stay out of it.

b.
although my father is not an activist, i have become involved in the gmo controversy, but i remain respectful of my father's position.

c.
my mother is not in favor of mandatory labeling, but my sister supports mandatory labeling.

d.
unlike my mother, i don't care to get involved in the gmo controversy.