A. 运转平衡、无困液现象 B. 结构简单,自吸性能较好 C. 对油液污染不敏感,维护方便 D. 流量、压力脉动较大
A. a fictitious sun moving along the celestial equator B. the visible sun moving along the ecliptic C. the Moon's motion in relation to the Sun D. the movement of the first point of Arie