* 圆管层流运动过流断面上的最大流速 umax 与平均流速 v 之比 umax:v=   。

A、<span style="font-size:16px;font-family: &#39;Times New Roman&#39;,&#39;serif&#39;">4&nbsp;</span>

B、<span style="font-size:16px;font-family: &#39;Times New Roman&#39;,&#39;serif&#39;">3</span>

C、<span style="font-size:16px;font-family: &#39;Times New Roman&#39;,&#39;serif&#39;">2</span>

D、<span style="font-size:16px;font-family: &#39;Times New Roman&#39;,&#39;serif&#39;">1</span>