フリー問題

問題文

What must the earliest concrete subclass of an incomplete type provide?

選択肢

1. It must supply bodies for all received bare declarations, and leaving one out unconditionally forces the subclass to stay abstract as well.
2. It must supply bodies for all received bare declarations, and leaving one out unconditionally forces the subclass to stay native as well.
3. It must supply bodies for all received signed fields, and leaving one out unconditionally forces the subclass to stay native as well.
4. It must supply bodies for all received signed fields, and leaving one out unconditionally forces the subclass to stay abstract as well.