Final answer:
The sentence is a complex sentence, comprising one independent clause and one dependent clause introduced by the subordinating conjunction 'before'.
Step-by-step explanation:
The sentence provided, "He was at the university before the Health Ministry's announcement on mandatory screening and home quarantine for all returnees from Beijing," is a complex sentence.
This is because the sentence consists of one independent clause, "He was at the university," and at least one dependent clause, "before the Health Ministry's announcement on mandatory screening and home quarantine for all returnees from Beijing." A complex sentence contains a main clause that can stand alone and a subordinate clause that cannot stand on its own. The dependent clause is introduced by the subordinating conjunction "before" which connects it to the main independent clause.
A simple sentence contains only one idea within a single main clause, which is not the case here, a compound sentence would have two or more independent clauses joined by a conjunction, and a compound-complex sentence would incorporate at least two independent clauses and one or more dependent clauses, which again, is not the case for the given sentence.