Which of the following is an appropriate characteristic of flash memory?
Select one:
a. Since data can be written only once, it is used as program memory, etc.
b. Although refresh cycles are required, it is used as main memory because of the capability of rewriting data any number of times.
c. Since it allows high-speed access, it is used as cache memory, etc.
d. Since it is rewritable and nonvolatile memory, it is used as USB memory or SD card.