In my opinion, the correct answer is <span>C. As Jake was reading the email from June yet again, the flight attendant coughed gently to get his attention.
A complex sentence has one independent clause (that can stand on its own), and two or more dependent (subordinate) clauses. In this case, the independent clause is "the flight attendant coughed gently to get his attention". The dependent one starts with a subordinator "as". The other options are compound sentences - made of two or more independent clauses which are connected with coordinators (but, and).</span>
