四冲程汽油机润滑的优点有（）。A、结构简单 B、机油冬夏通用 C、可按发动机工况提供
题型：多项选择题
问题：
四冲程汽油机润滑的优点有（）。
A、结构简单
B、机油冬夏通用
C、可按发动机工况提供机油
D、提高润滑特性
E、降低有毒废气排放
F、节省机油
题型：多项选择题
四开放作文 50 请根据下面提示，写一篇短文。词数不少于50. In your English class, the teacher shows the picture below and asks the class to discuss it. Your classmates may have different understandings. Look at the picture carefully and tell the class how YOU understand it.
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