Which of the following is an example of moderate-intensity activity?

Cycling 4 miles in 15 minutes is considered moderate-intensity activity because it generally elevates the heart rate to a level that allows for some conversation but requires more effort than just a leisurely pace. This intensity is typically associated with activities where participants may feel breathless but can still talk, indicating they are working at a moderate level of aerobic capacity.

In contrast, running a marathon and sprinting are higher intensity efforts that require significant exertion, often leading to an inability to maintain a conversation due to the high demand on the cardiovascular system. Similarly, jumping jacks for 5 minutes may not reach the sustained moderate intensity benchmark, depending on the individual's fitness level. Thus, cycling at that pace effectively hits the moderate-intensity mark, making it the correct answer.