How do arteries of pulmonary circulation differ structurally from the system arteries?

the pulmonary are more like veins anatomically. They've got very thin walls, reflecting the statement that  pulmonary circulation is low pressured

Generally spontaneous human combustion is something that still bewilders some, human combustion happens very rarely and doesn't affect the surrounding areas, so unless you want to set your self on fire, human combustion will remain spontaneous and very rare.

The answer here would be "work ethic."