多项选择题 WhichthreestatementsaboutSTPtimersaretrue？（）

单项选择题 Examine the diagram. A network administrator has recently installed the above switched network using 3550s and would like to control the selection of the root bridge. Which switch should theadministrator configure as the root bridge and which configuration command must theadministrator enter to accomplish this？（）

多项选择题 Given the above diagram and assuming that STP is enabled on all switch devices，  which two statements are true？（）