One of the following is true regarding FRC?

Correct Answer: C

Rationale: Functional residual capacity (FRC, ~2.5-3 L) is the lung volume post-normal expiration, a resting state where lung inward recoil balances chest wall outward recoil true for both lung and thorax, but not the focus. The true statement is that at FRC, intra-alveolar pressure equals atmospheric pressure (~760 mmHg), as no airflow occurs (gradient = 0), with muscles relaxed. Intrapleural pressure (IPP) is negative (~-4 mmHg, 756 mmHg) at FRC, not above atmospheric (760 mmHg), maintaining lung expansion false if elevated. Compliance isn't lowest at FRC (not listed). Alveolar-atmospheric equality is a core principle, ensuring rest stability, making it the standout truth, reflecting FRC's role as the ventilatory baseline.

Correct Answer: A

Rationale: The troposphere, extending ~0-12 km above Earth's surface, contains ~80% of atmospheric mass and nearly all weather phenomena clouds, rain, storms driven by solar heating, convection, and water vapor. The stratosphere (~12-50 km) holds the ozone layer, stable and dry, with minimal weather. The mesosphere (~50-85 km) is cold, with rare noctilucent clouds, not typical weather. The thermosphere (~85-600 km) is thin, hot from solar radiation, and weatherless. The troposphere's density and dynamics (e.g., Hadley cells) foster weather, per meteorological data (e.g., AMS), making it the key layer, distinct from higher, less active regions.

Correct Answer: C

Rationale: The lateral nasal wall's blood supply (A) includes the sphenopalatine (external carotid) and anterior ethmoidal (internal carotid) arteries, making A true. Innervation (B) via ophthalmic (V1) and maxillary (V2) branches of the trigeminal nerve is correct. Lymphatic drainage (D) to submandibular and retropharyngeal nodes aligns with nasal anatomy. However, venous drainage (C) primarily goes to the facial vein and pterygoid plexus, not mainly to the cavernous sinus via a large emissary vein that's more relevant to the dangerous triangle of the face or specific infections. Small connections exist via ethmoidal veins, but C overstates this route, making it the least accurate.

Correct Answer: C

Rationale: Failed to generate a rationale of 500+ characters after 5 retries.

Correct Answer: C

Rationale: Ectoderm forms the epidermis (C), the skin's outer layer, via surface ectoderm differentiation into stratified squamous epithelium. Blood (A) originates from mesoderm, specifically hemangioblasts in the yolk sac and later bone marrow. The dermis (B), beneath the epidermis, is mesodermal, arising from fibroblasts and connective tissue. The spleen (D) is also mesodermal, from mesenchyme in the dorsal mesogastrium. C is correct epidermis' ectodermal lineage, forming skin and neural structures, distinguishes it from the mesodermal origins of the others.