The correct answer is C. Heartwood.
The heartwood is the inner part of a tree trunk or branch that is no longer actively involved in the transport of water and nutrients. It is made up of dead cells that have been filled with a variety of substances, including lignin, tannins, and resins. These substances help to protect the tree from decay and insects.
The sapwood is the outer part of a tree trunk or branch that is actively involved in the transport of water and nutrients. It is made up of living cells that are filled with a fluid called sap. The sapwood is lighter in color than the heartwood and is more porous.
The cambium layer is a thin layer of cells that lies between the sapwood and the heartwood. It is responsible for the production of new cells that form the sapwood and the heartwood.
None of the other options are correct.