A.SELECT cust_last_name, cust_credit_limit FROM customers ORDER BY cust_credit_limit DESC
B.SELECT cust_last_name, cust_credit_limit FROM customers ORDER BY cust_credit_limit
C.SELECT cust_last_name, cust_credit_limit FROM customers ORDER BY cust_credit_limit NULLS LAST
D.SELECT cust_last_name, cust_credit_limit FROM customers ORDER BY cust_last_name, cust_credit_limit NULLSLAST