Plies can be radial, bias, or belted bias.
Plies are separate layers of rubber that make up the body of a tire. They are tied into bundles of wire called bead coils. Sidewalls connect the bead to the tread and protect the tire from curb impact. A ply rating tells you how much load the tire is expected to carry at a given pressure.
B Their job is to protect the tire from curb impact.
C A "ply rating" tells you approximately how long the tire should last.
D They connect the bead to the tread.