The _____ is an example of the female external genitalia.

A. the prostate: The prostate gland contributes approximately 25 to 30 percent of the total seminal volume. Its secretion is a milky, slightly acidic fluid containing citrate, enzymes, and prostate-specific antigen. While vital for sperm activation and liquefaction, it does not provide the majority of the fluid volume.

B. the pituitary: The pituitary gland is an endocrine organ located in the sella turcica of the sphenoid bone. It secretes gonadotropins like follicle-stimulating hormone and luteinizing hormone to regulate the reproductive system. It does not produce any components of the liquid semen ejaculated from the male reproductive tract.

C. the epididymis: The epididymis serves as the primary site for sperm maturation and storage where they acquire motility. While it adds a very small amount of fluid to support the sperm, its contribution to the final volume of ejaculate is negligible. It is a ductal structure rather than a major secretory gland.

D. the seminal vesicles: These paired glands produce about 70 percent of the total semen volume. The secretion is a viscous, alkaline fluid rich in fructose, prostaglandins, and clotting proteins. This fluid provides the primary energy source for sperm and helps neutralize the acidic environment of the female reproductive tract.

E. the bulbourethral glands: Also known as Cowper's glands, these small structures secrete a clear, alkaline mucus during sexual arousal. This pre-ejaculate lubricates the glans penis and neutralizes residual acidic urine in the urethra. Their contribution to the final volume of semen is usually less than 5 percent.

A. urobilin: This pigment is a metabolic byproduct of hemoglobin breakdown and is responsible for the characteristic yellow color of urine. Its presence is expected as the kidneys filter urobilinogen from the blood, which then oxidizes. It is a normal physiological component of human urinary waste.

B. magnesium: Electrolytes like magnesium are filtered at the glomerulus and partially reabsorbed in the tubules. The kidneys excrete excess magnesium to maintain systemic mineral homeostasis. Small amounts of this cation are consistently found in the urine of healthy individuals following normal dietary intake.

C. glucose: Under normal conditions, 100 percent of the glucose filtered at the glomerulus is reabsorbed by the proximal convoluted tubule. The presence of glucose in the urine, known as glycosuria, usually indicates hyperglycemia or a renal transport defect. Healthy urine should not contain detectable levels of glucose.

D. creatinine: Creatinine is a metabolic waste product of muscle metabolism that is filtered and not reabsorbed by the renal tubules. Its excretion is constant and serves as a reliable marker for assessing glomerular filtration rate. It is a standard and necessary component of healthy urine.

E. ammonia: Ammonia is produced by the tubular cells as a byproduct of amino acid deamination and acts as a buffer for hydrogen ions. It is excreted in the urine to help regulate the acid-base balance of the body. Its presence is a normal result of renal metabolic activity.