活塞环是汽缸镜面与活塞之间的密封零件同时起着（）作用，要求活塞环密封可靠耐磨性好。
Which of the following statements concerning cylinder liner wear is true?（） Liner wear is distributed equally between the upper and lower portions of the cylinder。 Excessive liner wear causes wear between piston ring and groove。 Excessive, but uniform liner wear will not cause wear between piston ring and groove。 Liner wear is normally greatest in the middle of the cylinder。
哈尔滨一号线最高试验速度为（）km/h，最高运行速度为（）km/h。
Horizontal fore or aft motion of a vessel is known as（）. pitch。 surge。 sway。 roll。
在被子植物细胞中，贮藏物质积累在：（） 所有类型的质体中。 线粒体中。 造粉体中。 叶绿体中。
用户满意度调查应注意（）
