题目

Women have a long way to go before they achieve full equality with men in the workplace, just _____ is often the case in many countries. A. as                   B. it                   C. what               D. that   答案：A如图，直二面角D-AB-E中，四边形ABCD是边长为2的正方形，AE=EB，F为CE上的点，且BF⊥平面ACE．（Ⅰ）求证AE⊥平面BCE；（Ⅱ）求二面角B-AC-E的大小；（Ⅲ）求点D到平面ACE的距离．