Which of the following activities is classified as aerobic activity?

Aerobic activity is defined as sustained physical activity that relies on the body’s ability to supply oxygen to working muscles over an extended period. Among the listed activities, cross country running fits this definition well because it involves continuous, rhythmic movement that elevates the heart rate for a significant duration, promoting cardiovascular endurance.

In contrast, swimming sprints are typically short, high-intensity bursts of activity that do not consistently elevate the heart rate over time, and thus are less aerobic in nature. Weightlifting primarily focuses on strength building through short, intense exertion, which emphasizes anaerobic energy systems rather than sustained aerobic effort. Yoga, while beneficial for flexibility and relaxation, typically does not elevate the heart rate to a level that would classify it as an aerobic exercise.

Due to its nature of prolonged movement that enhances cardiovascular fitness, cross country running is the clear classification of aerobic activity among the options given.