Well mostly they are: I, me, we, us, my, mine, our, ours, myself, ourselves.
Your answer would be D.) swam
Because 'climbed' is past tense and has no adverb (had, in this case), the correct conjugation of swim should be swam.
Hope this helps!
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").