The correct answers are:
- A Lord would be given land by the King in return for homage or a promise to serve the King when called upon;
The King was trying to keep close and satisfied the most influential people in the society, so he was playing on the card of giving them something from which they can profit, but in return they should give him support, be it economic, political, or military.
- A vassal dependent on the agricultural production of serfs to feed the whole system;
The whole system was dependent on the serfs and their performances in the agricultural field. If the serfs were doing the job properly, there was going to be enough food for everyone, but if not, and lets say that they wanted to rebel and stopped working in the fields, than the whole country would starve.
- A King would hire a vassal to provide an army and political advice during times of war;
The vassals were part of the aristocracy, and they were people that were educated, and had experience in combat and politics, so the King was very often calling upon them for advise during a war, or negotiations.