The HTTP 4xx error indicates a client-side issue, which in the context of Cloud Storage objects encrypted with customer-supplied keys (CSEK), can occur if the read operation is attempted without the necessary headers. Specifically, the request must include the base64-encoded key (x-goog-encryption-key) and the base64-encoded SHA256 hash of the key (x-goog-encryption-key-sha256) for validation. Option B is correct because omitting the SHA256 hash header would cause the server to reject the request, leading to a 4xx error. Option D is also correct because using the SHA256 hash of the key as the encryption key itself would result in a mismatch during validation, also causing a 4xx error. Given the question's structure with 4 options, the most directly correct answer is B, as it directly addresses the omission of a required header.