A block cipher mode of operation defines how a block cipher (such as AES) is applied to data longer than a single block, and how blocks are linked (or not linked) to provide certain security properties. ECB (Electronic Codebook) is one of the canonical block cipher modes: it encrypts each plaintext block independently using the same key. While ECB is generally discouraged because it leaks patterns (identical plaintext blocks produce identical ciphertext blocks), it is still a valid and historically important mode of operation and is often used as a teaching example of what not to do for structured data. In contrast, SHA-256 is a hash function (one-way digest) and not a mode for block ciphers. DSA is a digital signature algorithm and provides authenticity/integrity, not encryption mode behavior. RSA is an asymmetric cryptosystem, not a block cipher mode. Therefore, among the options, ECB is the correct example of a block cipher mode of operation.