清胃解毒汤常用于治疗（）水痘证。
参考答案：热毒重证
已知：D、E分别是△ABC边AB、AC上的点，DE∥BC，AE=6，AD=3，AB=5，则AC=______．
I was reading attentively in my own room ________ suddenly he knocked at the door.
A．when
B．while
C．then
D．as
