My brother_____while he_______ his bike and hurt himself.
A:fell; was riding
B:fell; were riding
C:had fallen; rode
D:had fallen; was riding
典故“指鹿为马”出自《史记·秦始皇本纪》:“赵高欲为乱,恐群臣不听,乃先设验,持鹿献于二世,曰:‘马也,’二世笑曰:‘丞相误邪?谓鹿为马。’问左右,左右或默,或言马以阿顺赵高。”该典故反映的本质问题是( )