The noun 'traffic' is a concrete noun as a word for the vehicles, pedestrians, ships, or planes moving along a route; a word for a large number of vehicles at a given place; a word for a physical thing.

The noun 'traffic' is an abstract noun as a word for the business of buying and selling; a word for communication or dealings between persons or groups; a word for a concept.

The word 'traffic' is also a verb.

The word 'irregular' is both a noun and an adjective.

The noun irregular is a word for a piece of merchandise that contains a flaw, which is often sold at a reduced price; and a word for a soldier who does not belong to the armed forces of a country.

The noun form for the adjective irregular is irregularity.

No, the demonstrative pronouns are this, that, these, and those. However, the pronoun that is also a relative pronoun; the relative pronouns are who, whom, whose, which, and that.

In this sentence, that is a relative pronoun introducing the relative clause 'that may or may not be true'.

Yes, the word narrative is a noun, a singular common noun. The word narrative is also an adjective. Example sentences:

Noun: They presented a narrative on the voyage of Shackleton.

Adjective: Narrative poetry is one of my favorite forms of literature; I memorized 'The Cremation of Sam McGee' when I was in school and I can still recite parts of it today.

Joint ownership is shown by making the last word in the series possessive; for example:

• John and Joan's birthday is on the tenth.

Individual ownership is shown by making both (or all) parts possessive; for example:

• John's and Joan's birthdays are the tenth and eleventh, respectively.

The word author is a noun, a word for a writer of poetry or prose, a word for a person.

A pronoun is a word that takes the place of a noun in a sentence. The pronouns that take the place of the noun author are he or she as a subject, and him or her as an object, and his or her for the possessive. Examples:

When the author arrives, hewill be pleased with the display of his work.

The author is my aunt. She has been writing since I can first remember her.

Add the -'s to the end of the name James (singular), for example, Jim James's house.

The plural form, the James family are the Jameses, the plural possessive is the Jameses' house.

The apostrophe after the s of the plural noun brothers tells you that it is a possessive noun, a noun indicating that something in the sentence belongs to two or more brothers.

Examples:

My brothers' names are Mike and Max. (the names of the brothers)

The brothers' business is very successful. (the business of the brothers)

She made sandwiches for her brothers' lunch.