Which of the following is considered secondary data storage?

Flash drives are considered secondary data storage because they provide a means to store data persistently beyond the temporary storage offered by primary memory, such as RAM. Secondary storage devices are used to hold information long-term, allowing users to save and retrieve data even when the device is powered off. Flash drives are portable, non-volatile memory devices that utilize flash memory technology to store data, making them ideal for backing up files or transferring data between computers.

In contrast, cache memory is a type of fast, volatile memory that is used to temporarily hold frequently accessed data for quick retrieval by the CPU. Registers are small storage locations within the CPU that hold data temporarily during processing tasks. Expansion cards can include a variety of components, such as graphics or sound cards, which assist with specific functions but do not serve as storage devices. Thus, while these other options play important roles in computing, they do not fit the criteria for secondary data storage like flash drives do.