Thhe answer is your last option "led to decline in racist attitudes towards African American and imigrants"
I would say the answer is C
Answer:
the use of poison gas and machine guns
Explanation:
Aerial attacks weren't really a thing, unrestricted submarine warfare was a reason why the US joined the war but not a factor in high casualty rates, and blimps using direct artillery fire isnt as practical as machine guns and poison gas
