How was china reunited under the sui dynasty?

One of the most significant achievements of the Sui Dynasty was the re-unification of China after a period of 300 years. They managed to do this with multiple wars with some of the fragmented states, as well as making alliances, so the re-unification was performed by force in general. Since the Sui Dynasty was well known for the militaristic approach of things, it was no wonder that they used the militaristic approach to manage to maintain the country unified, stable, and safe.

the answer would be c