两产品重介质旋流器按其原料煤给入方式分为有压（）给煤式和无压（）给煤式2种。前一种为圆锥形重介旋流器，后一种为圆筒形重介旋流器。
参考答案：切线；中心
------Where did you first meet your boyfriend?
------It was in the department store ______ he worked.
A．which
B．that
C．what
D．where
超声波流量计测量较大的误差的原因？
