Because Party A said that he didn't know his grades, that is to say, the grades of Party B and Party C were excellent and good, so the grades of Party A and Party D were also excellent and good, and Party B looked at the grades of Party C, so if Party C was excellent, then Party B was good, if Party C was excellent, then Party B was excellent, and so on, while Party D looked at the grades of Party A, so if Party A was excellent, then Party D was good.

The correct answer is: d