Final answer:
Skin and stem cells are the cells that divide constantly to produce new cells; these include the epithelial cells in the epidermis and various types of stem cells capable of differentiation and self-renewal.
Step-by-step explanation:
The examples of cells that divide constantly to produce new cells are C) Skin cells and D) Stem cells. Skin cells, especially the epithelial cells in the epidermis, are known to divide frequently to replace those that are constantly sloughed off due to friction. On the other hand, stem cells have the unique ability to divide continually and regenerate new stem cells and can also differentiate into a variety of cell types to maintain tissue homeostasis. Liver cells and muscle cells do not divide constantly; liver cells can regenerate but do not do so continually, and most muscle cells do not divide after maturity with a few exceptions.