Answer: The right answer is the A) Compound-complex.
Explanation: Just to elaborate a little on the answer, it can be added that this is an example of a compound-complex sentence because it combines both. On the one hand, it is a compound sentence, since it is made up of two independent clauses joined by a coordinating conjunction and a comma: "Employee turnover has decreased significantly this quarter,<em> </em><em>so [...], </em>"you'll have to admit that his results are impressive." On the other hand, it is a complex sentence, since it combines a dependent clause ("even though you may question Sam's training methods") with an independent clause ("you'll have to admit that his results are impressive").
