Answer:
d. Flash
Step-by-step explanation:
A flash memory can be defined as an electronic non-volatile memory chip (storage medium) that is typically used on computer systems and other digital devices such as routers, USB flash drives, switches, digital cameras, mp3 players etc. A flash memory is an electronically erasable programmable read only memory (EEPROM) and as such data saved (written) on it can be erased electronically. Also, a flash memory do not require a source of power (electricity) to save or retain data through the use of a floating gate MOSFET (FGMOS) or floating gate transistor.
In this scenario, you are designing an internet router that will need to save it's settings between reboots. The type of memory that should be used to save these settings is a flash memory because it does not require power to write or save data.