Final answer:
Option b) 'This seneschal was married to a wife, by whom great evil came upon the land.' uses foreshadowing to hint at future conflict and tension in 'The Lay of Equitan.'
Step-by-step explanation:
The sentence from "The Lay of Equitan" that uses foreshadowing to create tension by hinting that something bad is going to happen is option b) "This seneschal was married to a wife, by whom great evil came upon the land." This sentence implies that the wife will be the source of significant trouble or misfortune, thereby setting the stage for future events and building anticipation and concern in the reader about what that evil might be.