Which of the following is a cardiovascular activity included in PRT?

The selection of running or marching as a cardiovascular activity included in Physical Readiness Training (PRT) is based on their role in improving overall cardiovascular endurance. These activities elevate the heart rate and promote increased blood circulation, which is essential for developing aerobic fitness. Engaging in running or marching helps build endurance, facilitating the body's ability to sustain prolonged physical activity.

In contrast, other activities listed serve different primary purposes. Circuit training incorporates a variety of exercises designed for strength, endurance, and sometimes flexibility, but it is not exclusively focused on cardiovascular fitness. Plyometrics emphasizes explosive strength and power through jumping and bounding movements rather than sustained cardiovascular benefits. Weight lifting mainly targets muscular strength and hypertrophy and is not inherently cardiovascular.

Thus, running or marching aligns specifically with aerobic exercise principles, making it the correct answer regarding cardiovascular activities in PRT.