COUNTABLE AND UNCOUNTABLES

There are countable and uncountable nouns in English.

Countable nouns:

Most of the nouns are countable. You can combine them with numbers, e.g one, two or three. Here is an example:
one pencil
two pencils
three pencils
etc.

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Uncountable nouns:

These nouns can't be combined with numbers. Here is an example:
water
If you want to express a quantity, you have to use a special phrase e.g. a glass of water.
NOTE:
Some nouns can be either countable or uncountable. We recommend to use a good dictionary. Here is an example: hair - hairs
You have some hairs on your T-shirt. (There might be 5 or 6 of them.)
Your hair looks lovely. (Here you think of the hairstyle.)