单击“产生随机数”按钮，产生30个随机数，要求：（1）每隔100毫秒产生1个随机数，（2）用进度条控件显示随机数产生的进度，（3）将这些数以字符串的形式添加到组合框中，（4）实现组合框中内容的选择、删除功能。-Generate random numbers " button, click"　generate 30 random numbers, and requirements: (1) every 100 milliseconds to generate a random number, (2) to show the progress of the random number generator with a progress bar control, (3) these the form of a string is added to the combo box, and (4) the content of the combo box select and delete functions.