Answer:
it increased the demand for land and slave labour
I Don't see any multiple choice answers but i'm going to take a gander and guess that the answer you are looking for is "<u>Coal</u>"
The lord would provide to the vassal land from which they could make money from and in return the vassal would contribute troops to the lords army. Sometimes vassals would also pay a small fee of grain or various other goods as a sort of tax for the land.
