问题：
Refer to the exhibit. Users from the Engineering VLAN complain that every time Business VLAN users have a network connectivity issue，the Engineering VLAN users usually have problems experiencing slow response or network connectivity problems. After troubleshooting， anunauthorized switch 2 was found.This unauthorized switch has been a regular problem， assuming the root bridge function under thespanning-tree domain and causing the Engineering VLAN to be unstable. Which three of these actionscould be suggested to fix the problem？（）
A . Upgrade Spanning Tree Protocol to Rapid Spanning Tree Protocol.
B . Change Business VLAN PCs to switch 1 and switch 4.
C . Force the root bridge to be switch 2， instead.
D . Adjust spanning-tree timers （max-age and forward-delay）.
E . Shut down all unused ports.
F . Use MSTP to separate the Engineering VLAN from the Business VLAN to optimize spanning-tree convergence time within each VLAN.
Refer to the exhibit. Users from the Engineering VLAN complain that every time Business VLAN users have a network connectivity issue，the Engineering VLAN users usually have problems experiencing slow response or network connectivity problems. After troubleshooting， anunauthorized switch 2 was found.This unauthorized switch has been a regular problem， assuming the root bridge function under thespanning-tree domain and causing the Engineering VLAN to be unstable. Which three of these actionscould be suggested to fix the problem？（）
● 参考解析
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