题目

如图，平行四边形ABCD中，∠B＝60°，AB⊥AC，AC的垂直平分线交AD于点E，△CDE的周长是15，则平行四边形ABCD的面积为（ ）A. B. 40 C. 50 D. 答案：【答案】D【解析】首先证明AD+CD=15,再证明AD=2CD,推出CD=5，AD=10,利用勾股定理求出AC即可解決问题;∵点E在AC的垂直平分线上∴EA=EC∴△CDB的周长=CD+DE+EC=CD+DE+EA=CD+DA=15∵四边形ABCD是平行四边形∴∠B=∠D=60°,AB∥CD∵AB⊥AC,∴AC⊥CD∴∠ACD=90°∴∠CAD=30°∴AD=2CD∴CD=5,AD=10∴AC=S =2S△ADC=2×5×5=25故选D______ that he can always make himself understood. A. So clearly he speaks English　　　 B. So clearly does he speak English C. Clearly as he speaks English　　　 D. As he speaks English clearly