Which of the following options is a drill exercise in the Army Physical Readiness Training?

The correct answer is the Single Leg Pushup, as it is specifically recognized for its application within the Army Physical Readiness Training framework. This exercise focuses on building upper body strength while also involving core stability. By performing the pushup on one leg, it challenges the individual not only to maintain strength but also balance and coordination, qualities that are important for soldiers in various physical demands and combat scenarios.

In contrast, while exercises such as the Squat Thrust, Jumping Jack, and Burpee are beneficial for overall conditioning and may be included in physical training regimens, they are generally categorized differently or may not be prioritized in the same way as the single leg pushup within the context of specific Army training drills. Each of these exercises has its own set of benefits, focusing on cardiovascular endurance, agility, or full-body conditioning, but they are not classified as formal drill exercises in the Army's specific training protocols as the Single Leg Pushup is.