k的定义式为<br/> A、<img src="https://static.zxtiku.com/wangke/imgs/topic/64c15d3330111eef627368f9072e65c0.jpg"/><br/> B、<img src="https://static.zxtiku.com/wangke/imgs/topic/f70f3da978da46b6900f8036808a1f9b.jpg"/><br/> C、<img src="https://static.zxtiku.com/wangke/imgs/topic/099be2fe8a2cc0e0fea57624a51ec2b7.jpg"/><br/> D、<img src="https://static.zxtiku.com/wangke/imgs/topic/05ce5b16627689f84eb24f6016ab1bda.jpg"/>