The singular and plural of nouns as attributives When most nouns are used as attributives, the number of attributive nouns does not depend on what the central noun is

The singular and plural of nouns as attributives When most nouns are used as attributives, the number of attributive nouns does not depend on what the central noun is

Use the singular, such as apple trees. Don't change the singular and plural of attributive nouns with the singular and plural of the central noun or countable and uncountable

Do nouns and adjectives have plural forms

Nouns as attributives are not subordinate relations, but usages. Usually singular numbers are used to modify nouns, but plural numbers are often used, such as sports shops and sales manager
Adjectives as attributives are partial positive relations
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How to distinguish the singular and plural forms of nouns when numeral + noun is used as attribute
Two dozen (twenty four eggs)
Ten mile walk
Two hundred trees
A five year plan
In this case, when the numeral + noun is used as attribute, the noun is singular, but in the following example, the plural is used as attribute, such as: a seven years child
How to distinguish?
When is the singular form? When is the plural. Please give me an example.

If you add "-" then you don't need to add the plural, for example: a ten minute break, not a ten minutes break, but sometimes it has to become the past tense, for example: a black skinned man, here means that the person's skin is black
And the a seven years child above you is wrong,
I hope it works