Concept:A possessive pronoun that stands alone is needed after the verb “is”.
Explanation:The subject is “I”, which is first person singular.
The blank comes after “is”, so it must be a possessive pronoun used without a following noun.
“Mine” means “my property” and fits correctly alone.
“My” needs a noun after it, like “my property”.
“Our” and “their” do not match the singular first-person subject “I”.
Answer:A. mine
I maintain that the property in question is
mine.