Which formal government structure was created during the middle ages

Feudalism, is the right answer.

Explanation:

Feudalism was a form of government that prevailed in most of the countries throughout the Middle ages. Initially, this system of feudalism began in Europe in the centuries between 9th and the 15th. In this type of government, the king or monarch gave a piece of land to the nobles and officers to maintain and in return of this, the noble or the leader has to maintain a ratio of soldiers and horse. Moreover, the noble had to pay some tributes to the ruler and supply him army at times of need.

the authority to tax.

c or d both can be the answer