[单选题]Catalyst 6500 (Catalyst OS系统)中设置主root的命令格式是______。

A．spanning-tree lan ＜vans＞ root primary

B．spanning-tree lan ＜vans＞ root secondary

C．set spantree root ＜vans＞

D．set spantree root secondary ＜vans＞