Correct or improve the translation of the following English sent

Correct or improve the translation of the following English sentences.原文: The oil used for lubrication must be of correct thickness. 译文：润滑油的厚度要适当。 改译：
【正确答案】：

润滑油的浓度要适当。

【题目解析】：thickness厚度、浓度。lubrication润滑，结合句意可知强调的是润滑油的浓度。