用液压泥炮堵铁口时，若油压低，表明打泥阻力小；反之，油压高，则阻力大。
参考答案：对
The man we followed suddenly stopped and looked as if ________ whether he was going in the right
direction.[ ]
A. seeing
B. having seen
C. to see
D. to have seen
心脏病孕妇最危险的时期
A．妊娠35～38周
B．妊娠32～34周
C．妊娠20～28周
D．妊娠28～32周
E．产后7天后
