The answer is : A bios or cmos jumper. The jumper acts as a switch by closing (or opening) an electrical circuit. Clearing the CMOS on your motherboard will reset your BIOS settings to their factory defaults. After clearing the CMOS, you'll need to access the BIOS setup utility and reconfigure your hardware settings.
B) a smokestack for an electric power plant
Downfolds are calles synclines. B is the correct choice.