Option (C) is the correct answer. The provided context explicitly defines stem cells as non-specialised cells (or unspecialised cells) that possess the inherent property of self-renewal via mitotic cell division and the potential to differentiate into a wide range of specialised cell types. Option (D) is incorrect because the text states stem cells are unspecialised. Options (A) and (B) are incorrect interpretations not supported by the biological definition provided in the text.