无效合同（）。 ["从发现无效时起无效","从法院判决无效时起无效","从仲裁机构裁决无效时起无效","从订立时起无效"]
《铁路旅客票价表》（）统称软席。 ["软座、软卧","硬座、硬卧","软座、硬卧","硬座、软卧"]
遇有工作失误，应向旅客（），不得强词夺理。 ["表示歉意","说明情况","解释清楚","承认错误"]
What is the function of the command switchport trunk native vlan 999 on a switch？（） ["It designates VLAN 999 for untagged traffic.","It blocks VLAN 999 traffic from passing on the trunk.","It creates a VLAN 999 interface.","It designates VLAN 999 as the default for all unkown tagged traffic."]
烧结料层中宏观上呈（）气氛。 ["还原","氧化","中性"]
物流与电子商物的关系？
