Final answer:
The sentence "Although Mayan cities were centers for religious activity, they may have had no permanent inhabitants" is a complex sentence with one independent clause and one subordinate clause.
Step-by-step explanation:
The sentence "Although Mayan cities were centers for religious activity, they may have had no permanent inhabitants" is a complex sentence.
A complex sentence contains one independent clause (a clause that can stand alone as a sentence) and one or more subordinate clauses (clauses that cannot stand alone as sentences).
In this sentence, the independent clause is "they may have had no permanent inhabitants," and the subordinate clause is "Although Mayan cities were centers for religious activity."