层管理只涉及某一层的管理对象，并利用（）的通信协议传递管理信息。
A、上一层
B、下一层
C、本层
D、所有层
参考答案：B
________ be a history teacher? [ ]
A. Did she used to
B. Does she use to
C. Did she use to
D. Does she used to
半透明纸
