A company wants to expand their storage capacity in a flexible manner over their existing network. Which of the following storage solutions would they consider?

An external RAID array attached to a server expands local storage for that server and does not inherently provide flexible expansion over the network to multiple clients or servers as a shared resource.

Network Attached Storage (NAS) provides file-level data access over a standard network like Ethernet and can be easily expanded, making it a flexible solution that leverages existing network infrastructure for shared storage.

A Storage Area Network (SAN) provides block-level storage typically over a dedicated high-speed network, which is generally more complex and not usually referred to as expanding storage 'over their existing network' in a simple, flexible manner.

A tape library is primarily an archival and backup solution, not designed for flexible, active storage capacity expansion for day-to-day operations.