在△ABC中，∠ACB是锐角，点D在射线BC上运动，连接AD，将线段AD绕点A逆时针旋转90°，得到AE，连接EC．

- Would you like some coffee?

- Yes, and please get me some milk. I prefer coffee __________ milk.

算一算

     11－9=____          14－9=____         17－9=____

     13－9=____          15－9=____         18－9=____