After the marketing department finished planning the campaign.
Explanation:
A subordinate or dependent clause is a sentence that cannot stand alone because they do not make a complete meaning. Such a clause has to rely on another main clause in order to make complete sense. The first option is a subordinate clause because it simply provides more information about an event. Even though it contains a subject and a verb, does not give the total information that is needed to understand what is being talked about.
