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.