Answer:
Adjective Clause: that sits on top of the hill
Words modified: house
Step-by-step explanation:
just did the assignment and got this question right with this answer, hope this helps!
also it looks like the answers you included with the question dont match up with the sentence "The old brick house that sits on top of the hill was built during the Civil War", my answer above coordinates with the sentence.
The sentence that goes with the answers you provided is "The gentleman who was sitting close to them was the senator from their home state," in which case the Adjective Clause: 'who was sitting close to them' and Word(s) modified: 'gentlemen' would be correct.