Both sides in World War I used what to cause death that is now banned?\nOptions:\n- homicide\n- poisonous gas\n- cyanide\n- nuclear weapons\n- massive weapons
Let's think now! Step-by-step reasoning:
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Posionous gas was used in the World war 1. Posionous gas can lead to death.
So, the final answer is poisonous gas.
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