World war i was more destructive than earlier wars because
a. the armies were more ruthless.
b. it lasted longer.
c. modern weapons were more deadly.
d. airplanes could drop huge bombs.

 C. modern weapons were more deadly.

In addition to machine guns and tanks and other conventional weapons, World War I also saw the introduction of chemical weapons in warfare.  An example of a deadly poison gas used was phosgene.  It was a colorless and odorless gas, so victims wouldn't know they were affected till it was too late.  After being exposed, victims lungs would start to fill with fluid and they would slowly suffocate over a couple days' time.