Of the four statements below, which is true? a. Expansion cards are nonvolatile memory chips that can be erased and rewritten.
b. Expansion cards are used to direct and coordinate most of the operations associated with local area network (LAN) and internet servers.
c. Expansion cards are the main circuit boards within a computer system.
d. Expansion cards are circuit boards that enhance the functions of a components of asystem unit and/or provide connections to peripherals.