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
I would say the first one
Possibly it depends on how good their eye sight is in the one eye i mean if a cyclops can do it then he should be able to
