Final answer:
Swimming is the modality of exercise that is not necessarily a form of resistance training, unlike weightlifting, bodyweight exercises, and yoga.
Step-by-step explanation:
The modality of exercise that is not necessarily a form of resistance training is b) Swimming. Resistance training involves activities that work against an external force, such as weights or resistance bands, to build strength and muscle. While swimming offers many cardiovascular and muscular benefits, it does not provide the same type of direct resistance that weightlifting, bodyweight exercises, or yoga do.