Final answer:
Samuel likely engaged in swimming, biking, and running, as these activities are what make up a triathlon and are essential for triathlon training. The correct option is b.
Step-by-step explanation:
The activities that Samuel performed each morning as he prepared for a triathlon are likely to be swimming, biking, and running. These are the three sports that comprise a triathlon and are essential for triathlon training. By engaging in these activities, Samuel would improve his endurance and ability to transition between each sport, both critical for a successful triathlon performance. Hence, b is the correct option.