What made the campaigns on the European and Middle Eastern frontiers even more horrific than those ...

What made the campaigns on the European and Middle Eastern frontiers even more horrific than those on the Western Front?
 
  A) Millions of civilians died from massacre, disease, starvation, and genocide.
  B) The soldiers were less plentifully equipped and supplied for modern warfare.
  C) The armies used million-shell artillery bombardments, poison gas, the earliest armored vehicles, and warplanes.
  D) The armies used barbed wire, machine guns, and counter-bombardments to hold up attackers.
  E) A single battle could go on for months and cost hundreds of thousands of lives.