The correct answer is: None of the above.
The first command executed when a computer is first turned on is the BIOS POST (Power-On Self Test). The BIOS POST is a series of tests that the BIOS performs to check the hardware on the computer and make sure that it is functioning properly. If the BIOS POST passes, the BIOS then loads the boot sector from the hard drive. The boot sector is a small program that is stored at the beginning of the hard drive. The boot sector is responsible for loading the operating system from the hard drive.
The options A, B, C, and D are all commands that are executed after the BIOS POST. Device=c:emm386.exe is a command that loads the EMM386 memory manager. EMM386 is a program that allows the computer to use extended memory. Device=c:doshimem.sys is a command that loads the DOSHIMEM memory manager. DOSHIMEM is a program that allows the computer to use expanded memory. Prompt=$p$g is a command that sets the command prompt. Patch c:dos is a command that patches the DOS kernel.
Therefore, the correct answer is: None of the above.