Answer:
The correct answer is: c, a complex sentence
Step-by-step explanation:
This is an example of a complex sentence. A complex sentence is compounded by two statements, one is the independent clause and the second one is the dependent clause. The first one can be a sentence alone, it does not need another statement to make sense, however the dependent clause cannot be a sentence by itself even though it has a subject and a verb, because it does not have sense by itself, it needs the independent clause to have a meaning
dependent clause: Although he was drafted into the Vietnam War
independent clause: Muhammad Ali refused to fight.