The correct answers are B) extreme pain and C) lung damage.
After the gas attack, the speaker describes victims as drowning," "yelling out," and "stumbling." Based on this description, the gas attack is harming soldiers in the following ways: extreme pain lung damage.
We are referring to the terrible effects of the so-called Mustard Gas during World War 1. During this war in Europe, armies used toxic gases or chemical weapons as part of their arsenal. Chemical gases caused so much damage to soldiers, civilians, and the environment, that was prohibited after the war in 1925, by the Geneva Protocol.