目前世界上已知最早的纸用什么原料制成[ ]
A．树皮
B．羊皮
C．麻
D．旧鱼网
答案：C
_____ I toured Lushan Mountain, I was deeply impressed with its beautiful scenery. [ ]
A. The first time
B. For the first time
C. At first
D. It was the first time
柴油机是通过调节发动机的（）来满足不同工况的需要。
A.喷油量
B.喷油时刻
C.混合气量
D.以上均不正确
