在柴油机润滑系统中，对机油进行第一次过滤的是（）
A.粗滤器
B.细滤器
C.集滤器
D.离心式滤清器
参考答案：C
I was much impressed by the modern life in Hong Kong ______ I came to visit this fantastic city. [ ]
A. at the first time
B. for the first time
C. by the first time
D. the first time
防爆型F扳手采用优质（）材料制作。
A.钢
B.铁
C.铜
D.铝
