Sebaceous glands secrete oil-like sebum for lubricating the hair and skin .
皮脂腺分泌油状皮脂润滑毛发和皮肤。
Although air is always present in lubricating oil , it is often justifiable to adopt measures to minimize its presence .
尽管在润滑油中经常有空气的”声影“，我们最好采取措施将其存在降低到最低。
When a lubricating oil becomes contaminated with water , its surface tension is lowered , thereby allowing bubbles in the oil to separate into smaller particles that are more easily suspended .
当润滑油液沾上了水后，表面张力降低，使得油液中的气泡分离成更小的微粒，这样就更容易悬浮。
Bad therapy based on bad theory is like a too-heavy oil that , instead of lubricating , can gum up the works - slowing everything down and heating everything up .
