Let's match the descriptions to the components of firearms and ammunition.
A. Metallic protrusion...: "Metallic protrusion where the primer gets compressed and explodes whilst the hammer strikes the primer". This describes the Anvil, a component inside a Boxer or Berdan primer against which the priming compound is crushed. So, A matches with III.
B. A cardboard or a plastic disc...: "A cardboard or a plastic disc of 12mm thickness to cushion the wad". This describes a filler or cushioning component within a shotgun shell, i.e., the Cushion Wad. So, B matches with II.
C. The steel block...: "The steel block which closes the breech in firearms". This is the definition of the Breech block, a part of the firearm's action, not the cartridge. So, C matches with I.
D. A cardboard or a plastic piece...: "A cardboard or a plastic piece inside the brass head of a shotgun cartridge". This describes the Base wad, which is located inside the shell head. So, D matches with IV.
The correct set of matches is A-III, B-II, C-I, D-IV.