The Company network utilizes the Multiple-instance Spanning Tree protocol in its switched LAN.   Which three statements about the MST protocol （IEEE 802.1S） are true？ （）

• A、 To verify the MST configuration， the show pending command can be used in MST configuration  mode.
• B、 When RSTP and MSTP are configured； UplinkFast and BackboneFast must also be enabled.
• C、 All switches in the same MST region must have the same VLAN-to-instance mapping， but  different configuration revision numbers.
• D、 All switches in an MST region， except distribution layer switches， should have their priority  lowered from the default value 32768.
• E、 An MST region is a group of MST switches that appear as a single virtual bridge to adjacent  CST and MST regions.
• F、 Enabling MST with the "spanning-tree modemst" global configuration command also enables  RSTP.