To make a switch always win the STP root election for VLAN 750, configure the lowest possible bridge priority for that VLAN. Cisco STP priorities are configured in increments of 4096, and priority 0 is the lowest configurable value. The command spanning-tree vlan 750 root primary is convenient, but it calculates a priority intended to beat the current root at the time the command is entered. It is not as absolute as setting priority 0. Several listed numeric values are invalid or too high to guarantee root status. Cisco CCNA 200-301 v1.1 Network Access tests this because root bridge placement is a core switching design control. A switch becomes root by having the lowest bridge ID, and priority is compared before MAC address. Setting the VLAN priority to 0 gives the switch the strongest possible election position for VLAN 750. The command that best guarantees root status is spanning-tree vlan 750 priority 0.