When this and that are used to modify nouns they treated a which part of speech?

When "this" and "that" are used to modify nouns, they are treated as demonstrative adjectives.

Here's why:

* Adjectives describe nouns: They provide more information about the noun they modify.

* Demonstrative adjectives point out specific nouns. They indicate which noun is being referred to.

Examples:

* This book is interesting. (This modifies the noun "book")

* I want that toy. (That modifies the noun "toy")

Let me know if you'd like more examples or explanations!