楚天千里清秋，____。（辛弃疾《水龙吟》）
如图所示，已知在三角形纸片ABC中，BC=3，AB=6，∠BCA=90°．在AC上取一点E，以BE为折痕，使AB的一部分与BC重合，A与BC延长线上的点D重合，则DE的长度为（ ）
There were two students in the class buildings during the earthquake, but of them failed to run out.
