Medium with worse lubricating property, such as light fuel oil, heavy fuel oil, coal tar, asphalt, viscose, emulsified mixture, etc.

润滑性较差的介质，如轻质燃油、重质燃油、煤焦油、沥青、粘胶液、乳化液等；

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Unlike the light-duty vehicle market, most medium- and heavy-duty truck purchasers operate on slim profit margins where fuel costs are a major factor in their economic survival.

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