SSL 握手层包括哪些协议？（） ["握手协议","告警协议","密钥改变协议","会话保持协议"]
梯形图中动合触点与母线连接的指令为（）。 ["LD","OR","AND","LD-DOT"]
一般标准麻花钻的顶角在（）左右。 ["108°","118°","140°","90°"]
在WX3000系列或WX6103的无线控制器模式下通过命令（）可以切换到交换板模式下。 [" oap connect slot 0"," oap connect slot 1"," [H3C]oap connect slot 0"," [H3C]oap connect slot 1 <\/h3c><\/h3c>"]
进行三等水准测量时，如果采用两次仪器高法观测，在每一测站上需变动仪器高为（）以上 ["20cm","10cm","5cm","25cm"]
钢材按用途分类，可分为结构钢和（）两大类。
