下列关于边界层的说法哪些是正确的（） ["边界层的厚度顺着流动方向是逐渐加厚的","边界层的流速在物体的表面流速为0，沿法线向外流速增加","边界层就是一层薄薄的空气层","边界层内的流速保持不变"]
某学生在用托盘天平测物体质量时，已将天平调好，估计物体质量约20g，将物体和砝码分别放入左右盘中后，发现指针偏向左侧，他应该（）。 ["减少砝码","增加砝码","向左移横梁右端的平衡螺母","向右移横梁右端的平衡螺母"]
按照《国家突发公共事件总体应急方案》的规定，我国突发公共事件III级代表（）。 ["一般","较大","特别重大","重大"]
What are two features of WCS wireless management？ （） [" centralized management for autonomous access points"," centralized management for lightweight access points"," integration with the Location Appliance to expand real time tracking to 1500 devices for 30 days"," integration with the Location Appliance to expand real time tracking to 2500 devices for 15 days"," the inclusion of an integrated AAA server"," an external AAA-server requirement"]
划分词类的语法标准是词的（），即词与词的（）。
当单位变动成本改变时，若其他因素不变，则保本销售量 （）。
