边界层流动中，边界层内流体的特性是：（） ["流速在物面法向上有明显的梯度，流动是有旋、耗散的","流速在物面法向上无明显的梯度，流动是有旋、耗散的","流速在物面法向上有明显的梯度，流动是无旋的","流速在物面法向上无明显的梯度，流动是无旋的"]
19世纪的三大发现是：细胞学说、（）以及能量守恒和转化定律。
在零部件自制或外购的决策中，如果零部件的需用量尚不确定，应当采用的决策方法是（）。
Which two characteristics are true of IVRs? （） [" They are known as fabric routing."," They cannot span multiple switches."," Their connectivity is supported by Layer 2."," They enable devices in different VSAN fabrics to communicate."," They require that multiple switch fabrics be merged before they can function."]
突破思维定势是（） ["创新的需要","人类进步的需要","科学发展的需要","新事物诞生的需要"]
现代汉字偏旁有哪些类别？举例说明。
