Camphor Is a 10-Carbon Odoriferous Natural Product Made from the Joining

Camphor is a 10-carbon odoriferous natural product made from the joining of two isoprene units plus the addition of a ketone. Shown below on the left is its chemical structure. On the right is shown the camphor structure with two particular chemical "units" circled. What is/are the name(s) of these two units?

A) Both chemical units are isoprene.
B) Both chemical units are styrene.
C) Both chemical units are isopropene.
D) The upper chemical unit is isopropene and the lower unit is styrene.