RSTP adds features beyond STP that enable ports to be used for a role if another port on the same switch fails. Which of the following statements correctly describe a port role that is waiting to take over for another port role? $($Choose two answers.$)$a$.$ An alternate port waits to become a root port.b$.$ A backup port waits to become a root port.c$.$ An alternate port waits to become a designated port.d$.$ A backup port waits to become a designated port.