The correct option is A) ‘This’. The words that are used in place of a noun are pronouns. The name of a person, place, animal, or item can be the noun that is replaced. The given statement, ‘____ is a chair’, requires the addition of a singular demonstrative pronoun. Among the given options, ‘this’ is the only correct choice for the singular third-person pronoun, as ‘these’ and ‘those’ are plural. Hence, making option (A) the required answer.