Which type of cells are unspecialized and able to renew themselves for long periods through cell division?

Stem cells are the correct choice because they are a unique type of cell characterized by their ability to remain unspecialized and retain the capacity to divide and self-renew for extended periods. This ability to differentiate into various specialized cell types under appropriate conditions is what makes them vital in developmental biology and regenerative medicine.

In contrast, neurons, red blood cells, and skin cells have specific functionalities and characteristics that limit their ability for renewal. Neurons, for example, are specialized cells responsible for transmitting nerve impulses and typically do not undergo division once they have matured. Red blood cells are produced in the bone marrow and have a finite lifespan in circulation; they do not divide but are instead continually replenished from stem cells. Skin cells, while they do undergo frequent turnover, are derived from stem cells and are not capable of indefinite self-renewal like stem cells are. Therefore, stem cells stand out as the primary cell type with both unspecialized characteristics and the long-term ability to undergo cell division.