1) The essential parts of a noun group
A noun group consists or at least the following elements: a determiner and a noun.
2) Other parts of a noun group.
A noun group can also contain one or more modifiers; a modifier is an adjective, an adjectival phrase, a secondary noun, a prepositional phrase or a relative clause.
The principal noun in a noun group is called the head noun.
Check this site: http://linguapress.com/grammar/grammar3.htm
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