单选31.属于体积流量计的是（  ）。

A、<span style="font-size:16px;font-family:宋体">电磁流量计&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;&nbsp;</span>

B、<span style="font-size:16px;font-family:宋体">差压式质量流量计</span>

C、<span style="font-size:16px;font-family:宋体">双涡轮式质量流量计&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;&nbsp;</span>

D、<span style="font-size:16px;font-family:宋体">角动量式质量流量计</span>