The Guidelines for Loan Risk Classification stipulates that loan classification should follow the following principles: (1) the principle of authenticity, and the classification should truly and objectively reflect the risk status of loans; (two) the principle of timeliness, the classification results should be adjusted dynamically according to the changes in the borrower's business; (3) Importance principle, which evaluates and classifies many factors that affect loan classification; (d) Prudence principle, for loans that are difficult to accurately judge the borrower's repayment ability, the classification level should be appropriately lowered, so AC is correct and BD is wrong. So the answer is AC.