Well, first lets start with what a declarative sentence is. the kind of sentence that makes a statement or “declares” something. For example “He walks dogs."
A possessive pronoun indicates possession, for example mine, yours, hers, theirs.
A demonstrative pronoun is a pronoun that identifies and specifies a noun or pronoun. This, that, these, those.
Knowing this, you can make a sentence using them all.
"He ate his yogurt that he had been waiting to eat for days."
