What made WWI so brutal?

Poison gas, machine guns, artillery bombardment, submarines air planes etc. were weapons of war that caused enormous damage. Some of them - e.g. artillery existed - long time but modern technologies made it much more destructive. Paradoxically the level of technology was also lacking in some ways.  

Explanation: Can you make me Brainlest if i get right?

after balancing the chemical equation, what are the coefficients for these compounds?

h2s      

⇒ 3

hno3    

⇒ 2

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answer; which categories of people are most at risk of becoming a criminals;