题目1单选题
物理层的主要功能是:<img src="https://tihai-oss-cloud.itihey.com/img/67bdcc401253e6a4fb36cc4610386c6c.png">A. 数据格式转换<img src="https://tihai-oss-cloud.itihey.com/img/adb32f902b89078dd2a38c75990d5a19.png">B. 在通信信道上传输原始比特流<img src="https://tihai-oss-cloud.itihey.com/img/d040d5464dd01a7fe645978d8f4e4ec8.png">C. 路由选择<img src="https://tihai-oss-cloud.itihey.com/img/fee8c0992f2802373a1f803a353a3cd1.png">D. 差错控制