The correct answer is a) stratum basale.
The stratum basale, also known as the basal layer, is the deepest layer of the epidermis. It is responsible for the production of new epidermal cells through the process of mitosis. These newly formed cells gradually move up through the layers of the epidermis as they mature. The other layers mentioned, including the stratum granulosum, stratum lucidum, and stratum corneum, do not participate in cell division. Instead, they mainly serve as protective layers, with the stratum corneum being the outermost layer composed of dead, flattened cells that eventually shed off.