Test and analysis: Levers can be divided into labor-saving lever, labor-saving lever and equal-arm lever, which can be judged from the relationship between force arm and resistance arm. The bigger the power arm, the more labor-saving, and the bigger the resistance arm, the more labor-saving. Because the power arm of AOB is larger than the resistance arm, AOB is a labor-saving lever. According to the balance condition of the lever, the bigger the power arm, the more labor-saving, so keep your hands away from the O point.