STP生成树协议在()状态开始学习MAC地址。
A、阻塞
B、监听
C、学习
D、转发
参考答案:C
I saw our headmaster _____ the new teacher.[ ]
A. shake hands with
B. shook hands for
C. shaking hand with
D. shake hands at
防止或减少焊接变形的措施是什么?