Which statement most accurately describes Pulmonary embolism?

A. Obstruction of pulmonary arteries, commonly by thrombus originating in deep veins. B. A multisystem autoimmune disease associated with diverse autoantibodies and organ involvement. C. Diffuse hepatic fibrosis with regenerative nodules and altered liver architecture. D. A macrocytic anaemia caused by impaired DNA synthesis, often from folate or vitamin B12 deficiency.