A small web application allows users to download files from a server. The code uses open() without any exception handling. When a user requests a non-existent file, the server crashes with a traceback and returns a 500 Internal Server Error to the client. The team needs to modify the code to handle this situation gracefully: if the file does not exist, the application should return a 404 Not Found response (by calling a function send_404()). The application should not catch unrelated exceptions like KeyboardInterrupt. Which modification is the most appropriate?