Will give brainleist which of the following best explains why the feudal system developed?

a.
more and more people in europe were demanding political rights, and the feudal system spelled out the rights each class of people should have.

b.
europeans wanted to curb the power of the church, and the feudal system made it clear that nobles would write local laws, organize courts, and collect taxes.

c.
viking raiders and armed bands threatened everyone, but kings had lost power and could not protect everyone. under the feudal system, nobles could protect their property and local people by offering land in exchange for loyalty and military service.

d.
as cities in europe grew, nobles realized they were losing their importance in society. the feudal system guaranteed that the nobles would remain at the top of the political and social pyramid.