C # Get the current file working path comparison between two ways

two ways to get or set the current work path in C #:

the difference between Application.startuppath and System.Environment.CurrentDirectory

For example, you can start the program on your desktop, but in the middle you use a OpenFileDialog to open a file in the folder of e disk named ABC, then currentdirectory becomes E:\ABC, So if you want to get a file on the Startup folder again, it's useless.

But Application.startuppath will not be like this, no matter which disk you open in the middle of the file, the boot path is on the desktop there, has not changed.