柴油机维修保养的“五忌”是什么?
参考答案:
(1)一忌降低喷油压力;
(2)二忌扩大引燃孔;
(3)三忌用煤油代替柴油;
(4)四忌火烧活塞销孔;
(5)五忌汽缸垫上抹黄油。
下列那一种情况不是由酸雨造成的?
A.森林枯萎
B.鱼虾死亡
C.水体富营养化
D.土壤肥力降低
Jane usually comes to school _______ bike, but sometimes she goes to school foot.[ ]
A. by; by
B. on; on
C. by; on
D. with; on