他们的性格截然相反，一个外向活泼，一个内向安静。

Their personalities are ___diametric opposites—one is outgoing and lively, while the other is introverted and quiet.

他在圆形饼干上画了一条直径线，准备平均分成两半。

He drew a ___diametric line on the round cookie to divide it evenly in half.