* 已知某变径有压管段的管径之比 d1/d2=0.5 ，则相应的雷诺数之比 Re1/Re2= =   。

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

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

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

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