$17.(2$ points$)$ Web development involves both server$-$side and front$-$end development. What functionalities can be achieved exclusively on the server$-$side that are impossible $($or highly imprac$-$tical$)$ to implement using front$-$end technologies $($HTML$,$ CSS$,$ and JavaScript$)?($Select all that apply$)$A$.$ Accessing and modifying data in a database.B$.$ Handling user authentication and authorization for secure access control.C$.$ Directly manipulating the Document Object Model $($DOM on the client$-$side.D$.$ Validating user input to ensure data integrity before processing.E$.$ Applying complex business logic and performing calculations.