The reason that transposition ciphers are easily recognizable is character. A transposition cipher is a type of cipher that rearranges or permutes the order or position of the characters or symbols in the plaintext, without changing or altering the characters or symbols themselves, to produce the ciphertext. A transposition cipher can help to conceal the meaning or content of the plaintext, by making it difficult or impossible to read or understand the ciphertext, without knowing the key or algorithm that was used to transpose the characters or symbols. However, a transposition cipher is also easily recognizable, as it does not change or alter the frequency or distribution of the characters or symbols in the plaintext, which can be used to identify or analyze the ciphertext. The reason that transposition ciphers are easily recognizable is character, which is the smallest unit or element of the plaintext or ciphertext, such as a letter, number, or symbol. Character is the reason that transposition ciphers are easily recognizable, as it is the basis or criterion for the transposition or permutation of the plaintext or ciphertext, as well as for the frequency or distribution analysis of the plaintext or ciphertext. Key, block, or stream are not the reasons that transposition ciphers are easily recognizable, as they are either more related to the encryption or decryption process, rather than the recognition or identification process, or to the other types of ciphers, such as substitution ciphers, which change or alter the characters or symbols in the plaintext, rather than rearrange or permute them. References: CISSP All-in-One Exam Guide, Eighth Edition, Chapter 5: Cryptography and Symmetric Key Algorithms, page 250; CISSP Official (ISC)2 Practice Tests, Third Edition, Domain 3: Security Engineering, Question 3.11, page 136.