Answer:
B. Atomic Weapons
Explanation:
Tanks were used near the end of WW1, with tanks such as the Renault FT, Mark 5, and the German A7Vs. Atomic weapons weren't even a concept back then. Gas was used since 1915, invented by a German scientist trying to develop a pesticide, and Machine guns such as the Vickers or MG08 were common in the trenches.
