To best help Marcus incorporate an anaerobic workout into his weekly schedule, he should consider Zumba or a similar high-intensity interval workout. While swimming and running can provide cardiovascular benefits and can be performed anaerobically depending on the intensity, Zumba (or "zumbucket") typically combines aerobic and anaerobic elements, particularly through high-intensity dance movements.
If he’s looking specifically for a workout focused on anaerobic benefits, High-Intensity Interval Training (HIIT) or resistance training could also be effective options to add. But among the choices given, Zumba would be a suitable anaerobic workout to include.