柴油机故障中，机油通过（）进入燃烧室，即“机油下窜”。
A.活塞杆
B.活塞环
C.气门导管
D.气门杆
参考答案：C
When the dispute over duty payment arises between the duty payer and the Customs, the duty payer should first pay the duty and then, within ______ of the issuance of the duty memo, apply to the Customs in writing for a reconsideration of the case.
A．10 days
B．20 days
C．30 days
D．one year
三个刚片两两之间由两个链杆相连接构成的体系是( )。
A．无多余约束的几何不变体系
B．瞬变体系
C．体系的组成不确定
D．几何可变体系
