MDK project, multiple startup files, how does KEIL identify which one to compile?

Multiple startup files

Adding multiple startup files by saying that compilation will be wrong. But this project passed very well … … how does keil recognize that you want to compile startup_stm32f10x_hd.s? It took half a day to notice the slight difference in the icon of those files.

startup_stm32f10x_hd.s There are no three red dots on the file icon for this file, indicating that it is now included in the project. Check out its configuration properties:

Note: Include in Target Build.

This means compiling this file at compile time. Several other files are unchecked, that is, they are not compiled.