PTN是指（） ["分组传送网","同步传送网","异步传送网","波分传送网"]
In an Ethernet network, under what two scenarios can devices transmit?（） [" when they receive a special token"," when there is a carrier"," when they detect no other devices are sending"," when the medium is idle"," when the server grants acce"]
因承运人责任使旅客不能按票面记载的日期、车次、座别、铺别乘车时，站、车（）。 ["不予办理","应重新妥善安排。","退票"]
目前采用重组DNA技术制造人胰岛素的两条途径为（）和（）。
载荷中心距
简述教师对班级成员的认知。
