A. To enhance Spanning Tree troubleshooting on multilayer switches
B. To reduce the total number of spanning tree instances necessary for a particular topology 
C. To provide faster convergence when topology changes occur in a switched network
D. To provide protection for STP when a link is unidirectional and BPDUs are being sent but not  received
E. None of the other alternatives apply

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.