I have a question regarding this question; for one of the questions it asks me a follow up question for b which says

What other independent variables could you include in this regression model to improve the fit?

What other independent variables could you include in this regression model to improve the fit? (i) company name, name of company that did the audit (ii) type of audit, amount of taxes reported by the company that is being audited (iii) type of audit, company name, amount of taxes reported by the company that is being audited (iv) company name, name of company that did the audit, amount of taxes reported by the company that is being audited - Select your answer - v