说明：  单击“和” 按钮，求两随机数的和，同时使“平均值”按钮可用；单击“平均值”按钮，求两随机数的平均值，且使“平均值”按钮禁用。
(Click "and" button, find the two random numbers and, at the same time so that the "average" button is available click the "average" button, find the average of two random numbers, and the "average" button disabled.)