Question

In exchange for land, a knight agrees to be a sort of sub-vassal to a vassal. This agreement was known as _____.

investiture
homage
tyranny
subinfeudation

Answer 1

Subinfeudation
(ignore these extra characters)

Answer 2

That agreement was known as subinfeudation. That's when a piece of land is given to a subtenant by the feudal tenant.