接入网的三层结构包括主干层、配线层和（）。
A.引入层
B.控制层
参考答案：A
磁场（磁通密度）线圈常数
—I'm sorry I didn't make it to your party last night. — ______. I know you're busy these days.
A. Of course B. No kiddingC. That's all right D. Don't mention it
