This is a question from Operating System chapter and more related to configure booting a system.
The given options for above question were:
What is modified when changing the system start-up boot sequence?
Correct Answer & Explanation
BIOS: the first action of a PC is copying the BIOS program from CMOS to RAM when you turn it on.
The BIOS program is responsible for detecting and listing the devices/components of a PC. It also perform some testing and error reporting at the basic level.
During the detection process it detects all the bootable devices and connections. At the last stage of BIOS activity it looks for booting information from the bootable devices it detected according to the boot sequence configured in the BIOS. If it finds the right information from any detected device then it initiates the OS loading from it.
Other options are not much relevant to the question. CONFIG.SYS has nothing to do regarding boot sequence. Autoexec.bat runs the specified commands when booting process completes. And COMMAND.COM is there to intreprete user commands. Command.com loads after the io.sys and dos.sys are loaded. Autoexec.bat and config.sys are loaded after the booting is completed.