(A) Mustard Gas
(B) Nuclear Bomb
(C) ** Old Tactics/New Weapons
(D) New Tactics/Old Weapons like rocks and sticks
EXPLANATIONS BELOW
Concept note-1: -One reason why the Civil War was so lethal was the introduction of improved weaponry. Cone-shaped bullets replaced musket balls, and beginning in 1862, smooth-bore muskets were replaced with rifles with grooved barrels, which imparted spin on a bullet and allowed a soldier to hit a target a quarter of a mile away.