A predicate noun is a noun or noun phrase that provides more information about the subject of the sentence. Here, 'chairman' is a predicate noun that provides further information about "Dan Ross" which is the subject of the given sentence. An article is omitted before the predicate noun denoting a unique position which can be held at one time by one person only hence option C is correct because the article is omitted before 'chairman'. Option A is incorrect as a change is made in the sentence. Options B and D are incorrect because the article is supposed to be omitted before the predicate noun 'chairman'.