曲面<img src="https://static.zxtiku.com/wangke/imgs/topic/26ce4ed527bcee7aa8a3ffef129df674.jpg"/>在点<img src="https://static.zxtiku.com/wangke/imgs/topic/e457836b85a570bc66b899e26850cf67.jpg"/>的法线为：（） A. <img src="https://static.zxtiku.com/wangke/imgs/topic/5d65b330c1e012d6df562837da6afada.jpg"/> B. <img src="https://static.zxtiku.com/wangke/imgs/topic/9d8d92625c56c87ea630ad5a91f6f4fa.jpg"/> C. <img src="https://static.zxtiku.com/wangke/imgs/topic/8a311efea7a2577dac2d5e448aacaefa.jpg"/> D. <img src="https://static.zxtiku.com/wangke/imgs/topic/d8da2be421092ee075f3ab87e7f2288d.jpg"/>