Hi! The sentence you gave is a complex sentence. For a sentence to be compound, it should contain multiple subjects or predicate. On the other hand, for it to be complex, a subordinate clause must be present.
We can notice that the clause "that were built under the city" is a clause that cannot stand alone thus this will tell us that the sentence is complex.
ANSWER: D. Complex
The child felt unloved
the rent is cheaper for an unfurnished apartment
the work i started last week is still unanswered
the back door was unlocked when i came home
two unmarried girls shared the apartment
john has a lot of unpaid bills
jane got some unpainted chairs and painted them herself
the question is unanswered
i take the unused can of paint back to the store
A. an adjective (because it's describing the subject)
