下列哪种疾病，无"肺动脉高压"表现（）
A.肺心病
B.Ebstein畸形
C.二尖瓣狭窄
D.二尖瓣关闭不全
E.进行性全腺泡性肺气肿
参考答案：B
凸轮控制器控制的电阻器是（）接法。
A、不对称
B、对称
C、单相
D、双相
In securing a towing cable，consideration must be given to letting go in an emergency. The possible whip of towlines when released can be overcome by（）.
A.increasing the shaft RPM prior to release
B.using a pelican hook for quick release
C.using preventers
D.using a short chain for the lead through the stern chock
