常规的服务人际距离有几种（）？ ["有2种","有4种","有3种"]
Which of the following statements describes the function of an air compressor intake filter?（） ["Protects against suction valve float","Provides a positive pressure on the air inlet valves","Prevents lubricating oil contamination of the compressed air supply","Protects against the damaging effects of airborne solid particle"]
下列属于商鞅变法内容的是（）。 ["奖励军功，禁止私斗","奖励耕织，重农抑商","普遍推行县制","按户口征收军赋"]
Hydraulic cranes must be properly warmed-up before being operated because （）. ["warm-up allows the hydraulic system to become charged with oil","warm-up allows the relief valves to be properly tested","hydraulic strainers operate only during the warm-up period","hydraulic fluid must be at the proper viscosity"]
按住鼠标左键同时移动鼠标到另一个位置的操作称为（）。 ["单击","双击","拖动","启动"]
从本质上来说，会展是为（）而进行的传播活动。会展的最大特点在于信息的（）。
