Which vein is indicated by the X in the picture below?

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A. Right lymphatic duct: the right lymphatic duct drains only the right upper quadrant (right head/neck, right arm, right thorax), not the majority of the body.
B. Jugular trunk: the jugular trunk drains head/neck regions; it does not itself drain the majority of the body.
C. Subclavian trunk: the subclavian trunk drains upper limbs; it is a trunk, not the single duct that collects most lymph from the body.
D. Thoracic duct: the thoracic duct collects lymph from the lower body, abdomen, left thorax, left head/neck, and left arm (the majority of the body) and empties into the left subclavian vein.

A. Microvilli: Microvilli increase surface area for absorption (common in intestines), not the hallmark of respiratory epithelium
B. Cilia: Respiratory epithelium (pseudostratified ciliated columnar) is equipped with cilia on its free surface to move mucus and trapped particles
C. Keratin: Keratinization occurs in skin epithelium (protective), not in the typical respiratory lining
D. Desmosomes: Desmosomes are cell junctions found in many epithelia but the question asks about free-surface specializations; cilia are the functional free-surface structures in respiratory epithelium