The amount of DNA present in the system of an organism that does not necessarily relate to how complex that certain organism is. There are single-celled microorganism with very few amount of DNA but are very complex with respect to arrangement of certain amino acid component of the DNA strands.
The third option: Increase the intensity of cardiovascular workouts, is the right one. we know this because the rest of the options don't give the right fit. anaerobic workout is a short burst of energy, so it wouldn't be a good fit. Doing fewer aerobic workouts would lower it even more. Decreasing intensity of a cardiovascular workout would also cause a larger decrease. so it is the third option. Hope this helps a lot.