The cytokines of the immune system, acting as signalers to adjacent cells, can provoke dangerous inflammation; the resultant autoimmune disease, characterized by cartilage and bone that become damaged although they are not actually attacked by the immune system, are known as "rheumatoid arthritis."

A) cartilage and bone that become damaged although they are not actually attacked by the immune system, are
B) cartilage and bone that become damaged although they are not actually attacked by the immune system, is
C) cartilage and bone that become damaged although the immune system does not actually attack them, are
D) damaged cartilage and bone although the immune system does not actually attack them, are
E) damaged cartilage and bone although they are not actually attacked by the immune system, is

OA is B

Why not E?