编写一个单文档的应用程序，当单击时，在消息窗口中显示“鼠标左键被按下！”，当右击时，则显示“鼠标右键被按下”。-Write applications in a single document, when clicked, displays in the message window, the left mouse button is pressed! , When you right-click, it will show the right mouse button is pressed.