According to Kothari, Leone, and Wasley (2005), a) The modified Jones model should be estimated cross-sectionally using at least ten firms with similar ROA. b) The modified Jones model should be estimated cross-sectionally using at least ten firms in the same 2-digit industry code. c) The modified Jones model should be estimated using the same company's time-series data using at least ten years of data. d) The modified Jones model should be estimated cross-sectionally using at least ten firms with similar firm sizes