题目

     Not only a popular singer was Yao Beina, but also she was an energetic and warm-hearted angel. She had her corneas (眼角膜) donated to two men who needed them, which helped them see the world clearly again.      Yao was born in a music family on Sept. 26, 1981 in Wuhan. She started to learn the piano at the age of 4, and she sang her first song on the stage when she was 9 years old.      She became well-known to the public after making a series of songs for the hit TV drama “The Legend of Zhenhuan” in 2012, and the mandarin version (中文版本) of “Let It Go” fr在Rt△ABC中，∠C=90°，AC=4，则AB•AC=（　　） A、-16B、16C、-9D、9