1.下面的方程中，图形是椭球面的为（）<br/> A、<img src="https://static.zxtiku.com/wangke/imgs/topic/0339e61042c8e866d8a767bd685bf826.jpg"/><br/> B、<img src="https://static.zxtiku.com/wangke/imgs/topic/3c5a01f0669adc5378633684a6f29abf.jpg"/><br/> C、<img src="https://static.zxtiku.com/wangke/imgs/topic/4a09da561d3320a8c3d3bed78922cd74.jpg"/><br/> D、<img src="https://static.zxtiku.com/wangke/imgs/topic/4d1dd8492cd7005d3a9f62711c40ec17.jpg"/>