What Prompted the Original Feudal Knights to Perform Their Duties

What prompted the original feudal knights to perform their duties?

A) They served because of an idealistic loyalty to their leaders.
B) The knights were motivated by chivalry and fulfilling romantic visionaries.
C) The knights were mercenaries who usually served the highest bidder in exchange for land and serfs.
D) They wanted to see justice and mercy balanced out in treatment of the serfs.
E) The knights were usually of a monastic order that saw its members as selfless servants of the people.