1.物质名词(water, air等)在用于一般意义时不加冠词：
Water boils at 100 centi degree.
水在摄氏100度沸腾。
We can't live without air.
没有空气我们就不能生活。
They make high-quality steel.
他们制造优质钢。
Snow covered the ground.
地上被白雪覆盖。
2.指该物质特定部分时可加定冠词：
The air (in the room) is bad.
(屋里)空气不好。
The water isn't very clean.
这水不太干净。
Don't stand in the rain.
别站在雨里。
Wipe off the dust.
把灰尘擦掉。
3.有时物质名词前还可加不定冠词，表示：
1)“一种”：
Marble is a precious stone.
大理石是一种珍贵的石料。
It was a special tea which tasted of chrysanthemum.
这足一种菊花茶。
2)“一场雨雪”：
What a heavy rain.
多大的雨呀。
It was bitterly cold, and a heavy snow was falling.
天气严寒，下着一场大雪。
3)“一份”：
A chocolate ice-cream for me!
给我一客巧克力冰淇淋。
An iced coffee for me.
给我一杯冰咖啡。
有时一个物质名词可表示可数的东西：
I need two yards of cloth.
我需要两码布。(不可数)
He wiped the books with a cloth.
他用一块布擦书。(可数)
