Answer: A. glomerulus.
Explanation:
Each kidney has about 1 million nephrons, the urine-forming unit, and each nephron is made up of a glomerulus (capillaries walls) and renal tubules. The glomerular is constituted by the capillaries walls, which branch out and form a network, covered by the Bowman's capsule that retains the liquid, and begin to form a sequence of tubes.
The blood reaches the kidneys through the renal artery, which branches into the afferent arterioles that attach to the glomerular capillaries (where blood is filtrated), then form the efferent arteriole, which again becomes capillaries - the peritubular capillaries, which surrounds the renal tubules.
The epidermis. It's the first layer of skin.
