cryptography/security engineering

Which of the following statements is correct regarding a general block cipher? Select one: a. A ciphertext block can be strictly longer than its corresponding plaintext block. b. A plaintext block can be strictly longer than its ciphertext block. c. The length of the key cannot be strictly smaller than the length of a plaintext block. d. The security of a block cipher is not affected by how often keys are renewed. e. The key length cannot be strictly bigger than the length of a plaintext block