题目

You know eating fruit and vegetables does good. But do you know it can also make you look good? People who increased their intake over just six weeks developed a healthy glow and appeared more attractive, researchers found. Scientists at St Andrews University found eating them slightly increased yellow and red pigments in the volunteers' skin. They monitored the food intake of 35 people and took pictures of their faces, arms and hands using a sensitive camera at the start, and after three and six weeks. Increasing their intake of greens by 2.9 portions a day was found to make the person如图所示，OA是以O为支点的杠杆，用力F沿AB方向拉杠杆，使杠杆平衡。请画出：①拉力F的示意图；②拉力F的力臂。