AP World History Exam Prep

Answer: D - Mustard gas was first employed in World War I, and caused physical effects, like skin blistering, that were horrifying to unaffected witnesses and victims alike. Chemical warfare was first practiced widely in World War I to combat entrenched troops. Mustard gas was not designed to cause fatalities as much as it was meant to disable an opponent or contaminate an area, though exposure could lead to death. Primarily, it burned the skin and mucous membranes, which was excruciatingly painful.