The most accurate response regarding the impact of feudalism after the fall of Western Rome is: "Feudalism was an effective protective measure against Germanic tribes."
Feudalism emerged as a social and economic system during the early Middle Ages, in part as a response to the instability and invasions from various groups, including Germanic tribes. It provided a structure for land ownership and protection, where lords offered land and protection to vassals in exchange for military service. This arrangement helped to stabilize society during a time of frequent invasions and warfare.
The other statements either misrepresent historical facts or are not wholly accurate regarding the origins and nature of feudalism.