Which of the following is an example of a solid-state storage device?

A USB flash drive is an example of a solid-state storage device because it uses flash memory to store data, as opposed to mechanical components. Solid-state devices are characterized by their lack of moving parts, which contributes to their durability, faster data access speeds, and typically lower power consumption compared to traditional hard drives.

In contrast, an external hard disk and a SATA hard drive both use spinning disks to read and write data, which classifies them as mechanical storage devices. An optical disc, such as a CD or DVD, also falls into a different category of storage since it uses laser technology to read and write data on a disc's surface. Therefore, the demonstrated speed, durability, and form factor of the USB flash drive distinctly highlight it as the solid-state option among the choices.