下述关于归一化方向性函数描述正确的是<br/> A、<img src="https://static.zxtiku.com/wangke/imgs/topic/41f21dba4e70b7edcb31e775534e3a3e.jpg"/><br/> B、<img src="https://static.zxtiku.com/wangke/imgs/topic/f950bf6771a5c0110984652c6ef60209.jpg"/><br/> C、<img src="https://static.zxtiku.com/wangke/imgs/topic/699dbbdda9c3a13947a857c0e4f44410.jpg"/><br/> D、<img src="https://static.zxtiku.com/wangke/imgs/topic/63f1277f7e8d1e376238699d4dfda172.jpg"/>