What is the best way to combine theses sentences using an appositive phrase? (the grand canal in china is a man-made waterway. it is the oldest in the world. the canal is still used today.)

a: the grand canal, which is the oldest man-made waterway in the world, is still used today.
b: the grand canal in china is a man-made waterway, still used, that is the oldest in the world.
c: the grand canal in china, the oldest man-made waterway in the world, is still used today.
d: the grand canal-which is and old, man-made waterway in china-is still used today.