用于润滑的()除具有抗热、抗湿基优良的润滑性能外,还能对金属表面起良好的保护作用。
A、钠基润滑脂
B、锂基润滑脂
C、铝基及复合铝基润滑脂
D、钙基润滑脂
参考答案:C
对象的图样填充分为()
A.双色填充
B.单色填充
C.全色填充
D.位图填充
It was in 1969 ______ two Americans went to the moon by spaceship.[ ]
A. when
B. that
C. at that time
D. just then