Step 1: Upon a first reading, doesn’t “such a model” sound a bit awkward? That’s a good clue that (A) is not the correct response. In fact, the original sentence contains two flaws. One is a grammatical error: the plural pronoun their is used to refer to the singular noun model. Either both should be plural or both should be singular, but they must match. The word their is not part of the underlined phrase, so look for an answer choice that uses models instead of model. (In grammatical terminology, the original sentence contains an error in “pronounantecedent agreement.”).
