曲面 <img src="https://static.zxtiku.com/wangke/imgs/topic/83e269fddbebaf4244c93a10f0c58425.jpg"/> 的面积为 ( ) . A. <br/> <img src="https://static.zxtiku.com/wangke/imgs/topic/4e98ab99aa4b559c50e64131c06f067c.jpg"/> ; B. <br/> <img src="https://static.zxtiku.com/wangke/imgs/topic/b0dfbf5072ce09daf870f781aee22ca2.jpg"/> ; C. <br/> <img src="https://static.zxtiku.com/wangke/imgs/topic/9b092ec1165352fa7a76b42ba127f818.jpg"/> ; D. <br/> 2 .