Final answer:
The epidermis is the outermost layer of the skin, serving as a protective barrier and lacking blood supply; thus, the answer is d. epidermis.
Step-by-step explanation:
The outermost layer of the skin is the epidermis. This layer is relatively thin, consists of cells filled with keratin, and lacks blood supply. The primary function of the epidermis is to act as a protective barrier against water and pathogens. Below the epidermis is the dermis, which is considerably thicker and contains blood vessels, sweat glands, hair follicles, and other structures such as sebaceous glands.
The inner layer that lies directly above the fatty layer or hypodermis is the dermis, which contains living cells and is vascularized. Therefore, the correct answer to the question 'Which of the following is the outermost layer of the skin?' is d. epidermis.