Question

hitler increased the size of germanys military in part by introducing a
conscription law.
series of war taxes.
propaganda blitz.
voluntary draft.

Explanation:

Hitler expanded Germany's military in violation of the Treaty of Versailles, and a key method was reintroducing mandatory military service via a conscription law. War taxes funded the military but did not directly increase troop numbers; propaganda boosted support but did not grow the military's size; a voluntary draft would not have rapidly expanded the force to the scale Hitler achieved.

Answer:

conscription law.