题目

—Your hat is so cool.Could you tell me_________ ? —At the shop beside our school. A.when you bought it         B.when did you buy it C.where you bought it        D.where did you buy it 答案：C（2012•宁城县模拟）如图，ABCD是边长为1的正方形，DE⊥平面ABCD，AF∥DE，DE=2AF．（Ⅰ）求证：AC⊥平面BDE；（Ⅱ）求点F到平面BDE的距离．