Final answer:
The sentence "You will have great responsibilities if you become an air traffic controller" is a complex sentence.
Step-by-step explanation:
The sentence "You will have great responsibilities if you become an air traffic controller" is an example of a complex sentence. A complex sentence consists of one main clause (independent clause) and one or more subordinate clauses (dependent clauses). In this sentence, the main clause is "You will have great responsibilities" and the subordinate clause is "if you become an air traffic controller". The subordinate clause starts with the subordinating conjunction "if". Therefore, the correct answer is C. Complex sentence.