The political order under feudalism was dependent upon the relationship between lords and their vassals. The responsibility of the vassal included

A.
an oath of loyalty and a pledge of military service.
B.
an agreement to keep the lower classes under control.
C.
the payment of taxes to the king or queen of the country.
D.
the promise to spread the Christian faith to their lands.

A. an oath of loyalty and a pledge of military service.